This PDQ cancer information summary for health professionals provides comprehensive, peer-reviewed, evidence-based information about the use of aromatherapy and essential oils in the treatment of people with cancer. It is intended as a resource to inform and assist clinicians who care for cancer patients. It does not provide formal guidelines or recommendations for making health care decisions.

This summary is reviewed regularly and updated as necessary by the PDQ Integrative, Alternative, and Complementary Therapies Editorial Board, which is editorially independent of the National Cancer Institute (NCI). The summary reflects an independent review of the literature and does not represent a policy statement of NCI or the National Institutes of Health (NIH).

Overview

This cancer information summary provides an overview of the use of aromatherapy and essential oils primarily to improve the quality of life of cancer patients. This summary includes a brief history of aromatherapy, a review of laboratory studies and clinical trials, and possible adverse effects associated with aromatherapy use.

This summary contains the following key information:

• Aromatherapy is the therapeutic use of essential oils (also known as volatile oils) from plants (flowers, herbs, or trees) for the improvement of physical, emotional, and spiritual well-being.
• Aromatherapy is used by patients with cancer primarily as supportive care for general well-being.
• Aromatherapy is used with other complementary treatments (e.g., massage and acupuncture) as well as with standard treatments for symptom management.
• Essential oils are volatile liquid substances extracted from aromatic plant material by steam distillation or mechanical expression; oils produced with the aid of chemical solvents are not considered true essential oils.
• Essential oils are available in the United States for inhalation and topical treatment. Topical treatments are generally used in diluted forms.
• Aromatherapy is not widely administered via ingestion.
• The effects of aromatherapy are theorized to result from the binding of chemical components in the essential oil to receptors in the olfactory bulb, impacting the brain’s emotional center, the limbic system. Topical application of aromatic oils may exert antibacterial, anti-inflammatory, and analgesic effects.
• Studies in animals show sedative and stimulant effects of specific essential oils as well as positive effects on behavior and the immune system. Functional imaging studies in humans support the influence of odors on the limbic system and its emotional pathways.
• Human clinical trials have investigated aromatherapy primarily in the treatment of stress and anxiety in patients with critical illnesses or in other hospitalized patients. Several clinical trials involving patients with cancer have been published.
• Aromatherapy has a relatively low toxicity profile when administered by inhalation or diluted topical application.
• Aromatherapy products are not subject to approval by the U.S. Food and Drug Administration unless there is a claim for treatment of specific diseases.

Many of the medical and scientific terms used in the summary are hypertext linked (at first use in each section) to the NCI Dictionary of Cancer Terms, which is oriented toward nonexperts. When a linked term is clicked, a definition will appear in a separate window.

Reference citations in some PDQ cancer information summaries may include links to external websites that are operated by individuals or organizations for the purpose of marketing or advocating the use of specific treatments or products. These reference citations are included for informational purposes only. Their inclusion should not be viewed as an endorsement of the content of the websites, or of any treatment or product, by the PDQ Integrative, Alternative, and Complementary Therapies Editorial Board or the National Cancer Institute.

General Information

Aromatherapy is a derivative of herbal medicine, which is itself a subset of the biological or nature-based complementary and alternative medicine (CAM) therapies. Aromatherapy has been defined as the therapeutic use of essential oils from plants for the improvement of physical, emotional, and spiritual well-being.

Essential oils are volatile liquid substances extracted from aromatic plant material by steam distillation or mechanical expression. Oils produced with the aid of chemical solvents are not considered true essential oils, because the solvent residues can alter the purity of the oils themselves and lead to adulteration of the fragrance or to skin irritation.

Essential oils are made up of a large array of chemical components that consist of the secondary metabolites found in various plant materials. The major chemical components of essential oils include terpenes, esters, aldehydes, ketones, alcohols, phenols, and oxides, which are volatile and may produce characteristic odors. Different types of oils contain varying amounts of each of these compounds, which are said to give each oil its particular fragrance and therapeutic characteristics. Different varieties of the same species may have different chemotypes (different chemical composition of the same plant species as a result of different harvesting methods or locations) and thus different types of effects.[1]

Synthetic odors are often made up of many of the same compounds, which are synthesized and combined with other novel odor-producing chemicals. However, synthetic fragrances frequently contain irritants, such as solvents and propellants, that can trigger sensitivities in some people.[2-4] Most aromatherapists believe that synthetic fragrances are inferior to essential oils because they lack natural or vital energy; however, this has been contested by odor psychologists and biochemists.[5]

Aromatherapy is used or claimed to be useful for a vast array of symptoms and conditions. A book on aromatherapy in children suggests aromatherapy remedies for everything from acne to whooping cough.[6] Published studies regarding the uses of aromatherapy have generally focused on its psychological effects (used as a stress reliever or anxiolytic agent) or its use as a topical treatment for skin-related conditions.

A large body of literature has been published on the effects of odors on the human brain and emotions. Some studies have tested the effects of essential oils on mood, alertness, and mental stress in healthy subjects. Other studies investigated the effects of various (usually synthetic) odors on task performance, reaction time, and autonomic parameters or evaluated the direct effects of odors on the brain via electroencephalogram patterns and functional imaging studies.[7] Such studies have consistently shown that odors can produce specific effects on human neuropsychological and autonomic function and that odors can influence mood, perceived health, and arousal. These studies suggest that odors may have therapeutic applications in the context of stressful and adverse psychological conditions.

Practitioners of aromatherapy apply essential oils using several different methods, including (1) indirect inhalation via a room diffuser or drops of oil placed near the patient (e.g., on a tissue), (2) direct inhalation used in an individual inhaler (e.g., a few drops of essential oil floated on top of hot water to aid a sinus headache), or (3) aromatherapy massage, which is the application to the body of essential oils diluted in a carrier oil. Other direct and indirect applications include mixing essential oils in bath salts and lotions or applying them to dressings. Different aromatherapy practitioners may have different recipes for treating specific conditions, involving various combinations of oils and methods of application. Differences seem to be practitioner-dependent, with some common uses more accepted throughout the aromatherapy community. Training and certification in aromatherapy for lay practitioners is available at several schools throughout the United States and United Kingdom, but there is no professional standardization in the United States, and no license is required to practice in either country. Thus, there is little consistency in the specific treatments used for specific illnesses among practitioners. This lack of standardization has led to poor consistency in research on the effects of aromatherapy, because anecdotal evidence alone or previous experience has driven the choice of oils, and different researchers often choose different oils when studying the same applications. However, there are now specific courses for licensed health professionals that give nursing or continuing medical education contact hours, including a small research component and information on evaluating/measuring outcomes.

The National Association for Holistic Aromatherapy (NAHA) (www.naha.org/) and the Alliance of International Aromatherapists (www.alliance-aromatherapists.org) are the two governing bodies for national educational standards for aromatherapists. NAHA is taking steps toward standardizing aromatherapy certification in the United States. Many schools offer certificate programs approved by NAHA. A list of these schools can be found on the NAHA website (https://www.naha.org/education/approved-schools/). National examinations in aromatherapy are held twice per year.

The Canadian Federation of Aromatherapists has established standards for aromatherapy certification in Canada (www.cfacanada.com/). They also have standards for safety and professional conduct and a public directory of certified aromatherapists. Other countries may have similar organizations.

Although essential oils are given orally or internally by aromatherapists in France and Germany, use is generally limited to inhalation or topical application in the United Kingdom and United States. Nonmedical use of essential oils is common in the flavoring and fragrance industries. Most essential oils have been classified as GRAS (generally recognized as safe), at specified concentration limits, by the U.S. Food and Drug Administration (FDA). (Refer to the International Federation of Aromatherapists website [www.ifaroma.org/] for a list of international aromatherapy programs.)

Aromatherapy products do not need approval by the FDA.

History

Proponents of aromatherapy report that aromatic or essential oils have been used for thousands of years as stimulants or sedatives of the nervous system and as treatments for a wide range of other disorders.[1] They link it historically to the use of infused oils and unguents in the Bible and ancient Egypt,[1] remedies used throughout the Middle Ages and the Renaissance,[2] and the burning of aromatic plants in various religious rites. The current applications of aromatherapy did not come about until the early 20th century when the French chemist and perfumer Rene Gattefosse coined the term aromatherapy and published a book of that name in 1937.[2] Gattefosse proposed the use of aromatherapy to treat diseases in virtually every organ system, citing mostly anecdotal and case-based evidence.[2]

Although Gattefosse and his colleagues in France, Italy, and Germany studied the effects of aromatherapy for some 30 years, its use went out of fashion midcentury and was rediscovered by another Frenchman, a physician, Jean Valnet, in the latter part of the century. Valnet published his book The Practice of Aromatherapy in 1982,[3] at which time the practice became more well-known in Britain and the United States. Through the 1980s and 1990s, as patients in Western countries became increasingly interested in complementary and alternative medicine (CAM) treatments, aromatherapy developed a following that continues to this day. In addition to the growing use of essential oils by nurses and aromatherapy practitioners for specific medical issues, the popularity of aromatherapy has also been exploited by cosmetics companies that have created lines of essential oil-based (although often with a synthetic component) cosmetics and toiletries, claiming to improve mood and well-being in their users.

Despite the growing popularity of aromatherapy in the latter part of the 20th century (especially in the United Kingdom), little research on aromatherapy was available in the English-language medical literature until the early or mid-1990s. The research that began to appear in the 1990s was most often conducted by nurses, who tended to be the primary practitioners of aromatherapy in the United States and United Kingdom (although it is dispensed by medical doctors in France and Germany). Aromatherapists now publish their own journal, the International Journal of Essential Oil Therapeutics. Also, many studies regarding the effects of odor on the brain and other systems in animals and healthy humans have been published in the context of odor psychology and neurobiology (and in the absence of the specific term aromatherapy).

In addition to topical antimicrobial uses,[4] aromatherapy has also been proposed for use in wound care [5,6] and to treat a variety of localized symptoms and illnesses such as alopecia, eczema, and pruritus.[7-9] Aromatherapy has also been studied via inhalation for airway reactivity.[10]

Studies on aromatherapy have examined a variety of other conditions: sedation and arousal;[11,12] startle reflex and reaction time;[13,14] psychological states such as mood, anxiety, and general sense of well-being;[15-29] psychiatric disorders;[30] neurologic impairment;[23] chronic renal failure;[24] agitation in patients with dementia;[31-35] smoking withdrawal symptoms;[36,37] motion sickness;[38] postoperative nausea;[39,40] nausea and emesis in combination with fatigue, pain, and anxiety in patients in labor;[25,26,41] pain alone;[42-45] and pain in combination with other symptoms.[22,23,25,26]

Published articles have described the use of aromatherapy in specific hospital settings such as cancer wards, hospices, and other areas where patients are critically ill and require palliative care for pain, nausea, lymphedema,[46,47] generalized stress, anxiety,[48] and depression.[49] These observational studies provide examples of the clinical uses of aromatherapy (and other CAM modalities), although they are generally not evidence based. Subjects have included hospitalized children with HIV,[50] homebound patients with terminal disease,[51] and hospitalized patients with leukemia.[52] Aromatherapy has also been used to reduce malodor of necrotic ulcers in cancer patients.[53]

Studies of aromatherapy use with mental health patients have also been conducted.[54] Most of the resulting articles describe successful incorporation of aromatherapy into the treatment of these patients, although outcomes are clearly subjective.

Theories about the mechanism of action of aromatherapy and essential oils differ, depending on the community studying them. Proponents of aromatherapy often cite the connection between olfaction and the limbic system in the brain as the basis for the effects of aromatherapy on mood and emotions; less is said about proposed mechanisms for its effects on other parts of the body. Most of the aromatherapy literature, however, lacks in-depth neurophysiological studies on the nature of olfaction and its link to the limbic system, and it generally does not cite research that shows these links. Proponents of aromatherapy also believe that the effects of the treatments are based on the special nature of the essential oils used and that essential oils produce effects on the body that are greater than the sum of the individual chemical components of the scents.

These assertions have been contested by the biochemistry and psychology communities, which take a different view of the possible mechanism of action of odors on the human brain (most do not differentiate the odors produced by essential oils from those of synthetic fragrances).[30] This neurobiological view, which focuses mostly on the emotional and psychological effects of fragrances (as opposed to the other symptomatic effects claimed by aromatherapists), takes into account what is known about olfactory transduction and the connection of the olfactory system to other central nervous system functions, including memory; however, it is primarily theoretical because of the lack of significant research addressing this topic.

Laboratory/Animal/Preclinical Studies

Numerous studies on the topical antibacterial effects of essential oils have been published; most have found the oils to have significant antimicrobial activity.[1] Some essential oils are antiviral and inhibit replication of the herpes simplex virus.[2] Other essential oils are fungistatic and fungicidal against both vaginal and oropharyngeal Candida albicans.[3]

Studies on rats in Europe and Japan have shown that exposure to various odors can result in stimulation or sedation, as well as changes in behavioral responses to stress and pain. A study [4] on the sedative effects of essential oils and other fragrance compounds (mostly individual chemical components of the oils) on rat motility showed that lavender oil (Lavandula angustifolia Miller [synonyms: Lavandula spicata L.; Lavandula vera DC.]) in particular had a significant sedative effect, and several single-oil constituents (as opposed to whole essential oils) had similarly strong effects. The authors do not comment on the presumed mechanism for this effect, although they suggest that the difference in results between the different oils (some of which were found to be stimulating, some sedative) is related to the “different chemical structures of the compounds…and functional groups…indicating the essential role of the volatility of the fragrance compounds and its bioavailability." The differences in bioavailability are ascribed to different levels of lipophilia, with the more lipophilic oils producing the most sedative effects. The researchers also found significant plasma levels of the fragrance compounds after inhalation, suggesting that the effects of aromatherapy result from a direct pharmacological interaction rather than an indirect central nervous system relay.

Other studies have investigated the effects of aromatherapy on rats’ behavioral and immunological responses to painful, stressful, or startling stimuli. In two European studies, rats exposed to pleasant odors during painful stimuli exhibited decreased pain-related behaviors, with some variation in response between the sexes.[5,6] Two studies from Japan showed an improvement in immunological and behavioral markers in rats exposed to fragrances while under stressful conditions.[7,8]

Human/Clinical Studies

No studies in the published peer-reviewed literature discuss aromatherapy as a treatment for cancer specifically. The studies discussed below, most of which were conducted in patients with cancer, primarily focus on other health-related conditions and on quality-of-life measures such as stress and anxiety levels.

A major review published in 2000 [1] focused on six studies investigating treatment or prevention of anxiety with aromatherapy massage. Although the studies suggested that aromatherapy massage had a mild transient anxiolytic effect, the authors concluded that the research done at that time was not sufficiently rigorous or consistent to prove the effectiveness of aromatherapy in treating anxiety. This review excluded trials related to other effects of aromatherapy (such as pain control) and did not include any studies looking at the effects of odors that were not specifically labeled as aromatherapy.

Several of the studies included in the Cochrane Database of Systematic Reviews are discussed in more detail. A randomized controlled pilot study examined the effects of adjunctive aromatherapy massage on mood, quality of life, and physical symptoms in patients with cancer.[2] Forty-six patients were randomly assigned to conventional day care alone or day care plus weekly aromatherapy massage using a standardized blend of oils (1% lavender and chamomile in sweet almond carrier oil) for 4 weeks. Patients self-rated their mood, quality of life, and the intensity of the two symptoms that were the most concerning to them at the beginning of the study and at weekly intervals thereafter. Of the 46 patients, only 11 of 23 (48%) in the aromatherapy group and 18 of 23 (78%) in the control group completed all of the 4 weeks. Patient-reported mood, symptoms, and quality of life improved in both groups, and there was no statistically significant difference between the two groups in any of these measures.

Another randomized controlled trial examined the effects of aromatherapy massage and massage alone on 42 patients with advanced cancer over a 4-week period.[3] Patients were randomly assigned to receive weekly massages with or without aromatherapy; the treatment group (aromatherapy group) received massages with lavender essential oil (Lavandula angustifolia Miller [synonyms: Lavandula spicata L.; Lavandula vera DC.]) and an inert carrier oil, and the control group (massage group) received either an inert carrier oil alone or no intervention. The authors reported no significant long-term benefits of aromatherapy or massage in pain control, quality of life, or anxiety, but sleep scores (as measured by the Verran and Snyder-Halpern sleep scale) improved significantly in both groups. The authors also reported statistically significant reductions in depression scores (as measured by the Hospital Anxiety and Depression Scale [HADS]) in the massage-only group.

A placebo-controlled, double-blind, randomized trial conducted in Australia investigated the effects of inhalation aromatherapy on anxiety during radiation therapy.[4] A total of 313 patients receiving radiation therapy were randomly assigned to one of three groups: carrier oil with fractionated oils, carrier oil only, or pure essential oils of lavender, bergamot (Citrus aurantium L. ssp. bergamia [Risso] Wright & Arn. [Rutaceae]; [synonym: Citrus bergamia Risso]), and cedarwood (Cedrus atlantica [Endl.] Manetti ex Carriere [Pinaceae]). All three groups received the oils by inhalation during their radiation therapy. The authors reported no significant differences in depression (as measured by HADS) or psychological effects (as measured by the Somatic and Psychological Health Report) between the groups. The group that received only the carrier oil showed a statistically significant decrease in anxiety (as measured by HADS) compared with the other two groups.

Another randomized controlled trial investigated the effects of massage or aromatherapy massage in 103 cancer patients who were randomly assigned to receive massage using a carrier oil (massage group) or massage using a carrier oil plus the Roman chamomile essential oil (Chamaemelum nobile [L.] All. [synonym: Anthemis nobilis L.]) (aromatherapy massage group).[5] Two weeks after the massage, the authors found a statistically significant reduction in anxiety in the aromatherapy massage group (as measured by the State-Trait Anxiety Inventory) and an improvement in symptoms (as measured by the Rotterdam Symptom Checklist [RSCL]; the subscales with improved scores were psychological, quality of life, severe physical, and severe psychological). The authors reported that the massage-only group showed improvement on four RSCL subscales; however, these improvements did not reach statistical significance.

In a placebo-controlled, double-blind, randomized trial of bergamot inhalation aromatherapy compared with a pleasant smelling shampoo that did not contain essential oils, administered at the time of stem cell infusion in 37 children and adolescents undergoing stem cell transplant, aromatherapy was not found to be beneficial in reducing nausea, anxiety, or pain.[6] As administered in this study, bergamot inhalation aromatherapy may have contributed to persistent anxiety after the infusion of stem cells. Although no more effective than placebo, parents receiving aromatherapy showed a significant decrease in their transitory anxiety during the period between the completion of their child’s infusion and 1 hour after infusion. Nausea and pain subsided over the course of the intervention for all children, although nausea remained significantly greater in patients receiving aromatherapy. These findings suggest that the diffusion of bergamot essential oil may not provide suitable anxiolytic and antiemetic effects among children and adolescents undergoing stem cell transplantation. The double blinding of the trial may explain the results, as single-blinded or nonblinded trials in general supported the aromatherapy intervention.

A similar study evaluated the efficacy of an aromatherapy intervention for reduction of symptom intensity of nausea, retching, and/or coughing among adult patients receiving stem cells preserved in dimethyl sulfoxide. The study found that an intervention of tasting or sniffing sliced oranges was more effective at reducing symptom intensity than an orange essential oil inhalation aromatherapy.[7]

A randomized controlled crossover clinical trial investigated the effect of inhaled ginger essential oil on alleviating chemotherapy-induced nausea and vomiting in Asian women with breast cancer.[8] Aromatherapy administered as inhaled ginger essential oil for 5 days was associated with small, statistically significant, but not clinically significant, reductions in acute nausea but had limited effects on reducing vomiting or delaying nausea in 60 evaluable patients.

A study whose primary objective was evaluating an aromatherapy service following changes made after an initial pilot at a U.K. cancer center also reported on the experiences of patients referred to the service.[9] Of 89 patients originally referred, 58 completed six aromatherapy sessions. The authors reported significant improvements in anxiety and depression (as measured by HADS) at the completion of the six sessions, as compared with before the six sessions. A small study examined the physical and psychological effects of aromatherapy massage in eight patients with primary malignant brain tumors attending their first follow-up appointment after radiation therapy.[10] The author reported no psychological benefit in these patients from aromatherapy massage (as measured by HADS) but reported a statistically significant reduction in blood pressure, pulse, and respiratory rate.

Antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus, are an increasing problem worldwide, causing intractable wound infections. Mixtures, such as those containing the volatile oils of lemongrass, eucalyptus, melaleuca, clove, and thyme with butylated hydroxytoluene, triclosan (0.3%), and 95% undenatured ethanol (69.7%), are being investigated against MRSA in vitro. No clinical trials have been performed.[11]

Two topical MRSA eradication regimens were compared in hospital patients. A standard treatment, which included mupirocin 2% nasal ointment, chlorhexidine gluconate 4% soap, and silver sulfadiazine 1% cream was compared with a tea tree oil regimen (melaleuca), which included tea tree 10% cream and tea tree 5% body wash. Both treatments were administered for 5 days. Of 114 patients who received the standard treatment, 56 (49%) were cleared of MRSA carriage. Of 110 patients who received the tea tree oil regimen, 46 (41%) were cleared of MRSA carriage. In a small group of patients, the tea tree oil regimen was associated with a higher clearance rate of MRSA carriage in the axilla, groin, and wound sites, but the difference versus standard treatment was not significant.[12]

Adverse Effects

Safety testing on essential oils has shown minimal adverse effects. Several oils have been approved for use as food additives and are classified as GRAS (generally recognized as safe) by the U.S. Food and Drug Administration; however, ingestion of large amounts of essential oils is not recommended. In addition, a few cases of contact dermatitis have been reported, mostly in aromatherapists who have had prolonged skin contact with oils in the context of aromatherapy massage.[1] Some essential oils (e.g., camphor oil) can cause local irritation; therefore, care should be taken when applying them. Phototoxicity has occurred when essential oils (particularly citrus oils) are applied directly to the skin before sun exposure. One case report also showed airborne contact dermatitis in the context of inhaled aromatherapy without massage.[2] Often, aromatherapy uses undefined mixtures of essential oils without specifying the plant sources. Allergic reactions are sometimes reported, especially after topical administration. As essential oils age, they are often oxidized so the chemical composition changes. Individual psychological associations with odors may result in adverse responses. Repeated exposure to lavender and tea tree oils by topical administration was shown in one study to be associated with reversible prepubertal gynecomastia.[3] The effects appear to have been caused by the purported weak estrogenic and antiandrogenic activities of lavender and tea tree oils. Therefore, avoiding these two essential oils is recommended in patients with estrogen-dependant tumors. However, this is the first published report of this type of adverse effect when using products containing tea tree or lavender oils.

Summary of the Evidence for Aromatherapy and Essential Oils

To assist readers in evaluating the results of human studies of integrative, alternative, and complementary therapies for people with cancer, the strength of the evidence (i.e., the levels of evidence) associated with each type of treatment is provided whenever possible. To qualify for a level of evidence analysis, a study must:

• Be published in a peer-reviewed scientific journal.
• Report on a therapeutic outcome or outcomes, such as tumor response, improvement in survival, or measured improvement in quality of life.
• Describe clinical findings in enough detail that a meaningful evaluation can be made.

Separate levels of evidence scores are assigned to qualifying human studies on the basis of statistical strength of the study design and scientific strength of the treatment outcomes (i.e., endpoints) measured. The resulting two scores are then combined to produce an overall score. A table showing the levels of evidence scores for qualifying human studies cited in this summary is presented below. For an explanation of the scores and additional information about levels of evidence analysis of integrative, alternative, and complementary therapies for people with cancer, refer to Levels of Evidence for Human Studies of Integrative, Alternative, and Complementary Therapies.

Changes to This Summary (06/08/2017)

The PDQ cancer information summaries are reviewed regularly and updated as new information becomes available. This section describes the latest changes made to this summary as of the date above.

Human/Clinical Studies

Added text about a randomized controlled crossover clinical trial that investigated the effect of inhaled ginger essential oil on alleviating chemotherapy-induced nausea and vomiting in Asian women with breast cancer; aromatherapy administered as inhaled ginger essential oil for 5 days was associated with small, statistically significant, but not clinically significant, reductions in acute nausea but had limited effects on reducing vomiting or delaying nausea in 60 evaluable patients (cited Lua et al. as reference 8).

Summary of the Evidence for Aromatherapy and Essential Oils

Added text to Table 1 about a randomized controlled, single-blind, crossover clinical trial that investigated the effect of inhaled ginger essential oil on alleviating chemotherapy-induced nausea and vomiting in an Asian population with breast cancer (cited Lua et al. as reference 9).

This summary is written and maintained by the PDQ Integrative, Alternative, and Complementary Therapies Editorial Board, which is editorially independent of NCI. The summary reflects an independent review of the literature and does not represent a policy statement of NCI or NIH. More information about summary policies and the role of the PDQ Editorial Boards in maintaining the PDQ summaries can be found on the About This PDQ Summary and PDQ® - NCI's Comprehensive Cancer Database pages.

About This PDQ Summary