Aged <70 with primary operable unilateral invasive breast cancer (N0, M0)

Histological grade 1 or specific good prognosis tumours

Maximum tumour size 20mm

No previous cancer except adequately treated basal cell carcinoma of the skin

Excluded if pregnant or lactating

Excluded if other diseases precluded adequate surgery, adjuvant therapy, or follow-up

• Intervention arm (RT-): WLE (0.5–1cm clear margin). Tamoxifen 20 mg/day for 5 years
• Control arm (RT+): WLE (0.5–1 cm clear margin). Tamoxifen 20 mg/day for 5 years. Whole breast radiation total 40–50 Gy in 15–25 fractions.

Age >40 years

Tumour 20mm or less, grade 1 or 2. PR status positive. Low cell proliferation rate

Excluded if extensive intraductal component or axillary node metastases

Intervention arm (RT-): segmental breast resection (1 cm margins) and levels I and II dissection of ipsilateral axilla.

Control arm (RT+): segmental breast resection (1 cm margins) and levels I and II dissection of ipsilateral axilla. Whole breast radiotherapy total 50 Gy within 5 weeks using 2 Gy daily fractions.

≥70 years with stage I, N0, ER+ breast cancer

No history of cancer other than in situ cervical or non-melanoma skin cancer within 5 years

Initially included tumours up to 4cm but reduced to 2cm

Intervention arm (RT-): lumpectomy with a clear margin (no ink on tumour). 20 mg tamoxifen per day for 5 years initiated during or after irradiation.

Control arm (RT+): lumpectomy with a clear margin (no ink on tumour). 20 mg tamoxifen per day for 5 years initiated during or after irradiation. RT included tangential fields to the entire breast followed by an electron boost to the lumpectomy site.

≥65 years with T1-T2, N0 hormone receptor positive breast cancer

Receiving neoadjuvant hormonal treatment

Excluded if history of in-situ or invasive breast cancer of either breast or previous malignant disease in the past year, other than non-melanomatous skin cancer or carcinoma in situ of the cervix

Intervention arm (RT-): No details for breast conserving surgery procedures provided (except ≥1mm margins). Tamoxifen (20 mg daily for 5 years) as the standard adjuvant endocrine treatment but other forms allowed.

Control arm (RT+): No details for breast conserving surgery procedures provided (except ≥1mm margins). Tamoxifen (20 mg daily for 5 years) as the standard adjuvant endocrine treatment but other forms allowed. RT total dose 40–50Gy in 15–25 fractions over 3–5 weeks. Boost permitted but not required.

≤80 years with unifocal stage 1 invasive breast cancer

Intervention arm (RT-): sector resection and axilla dissected to levels I and II

Control arm (RT-): sector resection and axilla dissected to levels I and II. Radiotherapy total dose of 54Gy in 27 fractions

≥ 65 years with T0–2, N0 unilateral breast cancer

Receiving adjuvant endocrine therapy.

Medically suitable to attend for all treatments and follow-up.

Excluded if pure in situ carcinoma or previous/concurrent malignancy within 5 years other than non-melanomatous skin cancer or carcinoma in situ of cervix

Excluded if grade 3 cancer