The present multicenter, retrospective and prospective observational study, aims to evaluate an ultra-hypofractionated whole breast irradiation schedule (WBI, 26 Gy in 5 fractions), in order to confirm literature data (FAST-F study) in the clinical practice.

Patient population included women affected by early stage breast cancer (BC), both invasive and ductal carcinoma in situ, receiving ultra-hypofractionated WBI (with or without a tumor bed boost) after breast conserving surgery (BCS). Main exclusion criteria are mastectomy and regional nodal irradiation. Neoadjuvant and/or adjuvant systemic therapies are allowed. The primary otcome is acute and chronic toxicity evaluation. Secondary outcomes are: overall servival (OS), disease-free survival (DFS), rates of local and loco-regional recurrences, distant metastasis occurrence, cosmetic outcome and quality of life (QoL) assessment. Acute and late toxicities will be scored according to the Common Terminology Criteria for Adverse Events (CTCAE) scale version 5.0. Cosmetic assessment will be graded according to the Harvard scale. Frontal photographs of both breasts will be used to evaluate toxicity and cosmetic results. For QoL assessment the EORTC (European Organisation for Research and Treatment of Cancer), QLQ-C30 and EORTC-QLQ-BR23 questionnaires will be administered.

The present multicenter retrospective and prospective observational study aims to evaluate feasibility, toxicity, efficacy, cosmetic outcome and QoL in early stage BC patients treated with BC followed by ultra-hypofractionated WBI (with or without a tumor bed boost). This study was designed to confirm literature data (FAST-Forward trial) in the clinical practice ("real life"study). All enrolled patients will be treated with an ultra-hypofractionated WBI schedule (26 Gy delivered in 5 consecutive fractions, single dose 5.2 Gy), according to FAST-Forward trial. Whole breast irradiation should be followed or not by a tumor bed boost (sequential: 7.6 Gy in 2 consecutive fractions, single dose 3.8 Gy or simultaneous intergrated boost: 30 Gy in 5 consecutive fractions, single dose 6 Gy). Either three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) or helicoildal techniques are allowed. Breath control techniques may be used at the discretion of each partecipating centre. Main exclusion criteria are mastectomy and needs for regional nodal irradiation. Neoadjuvant and/or adjuvant systemic therapies are allowed.

The primary outcome of this study is acute and chronic toxicity evaluation. Secondary outcomes are: OS, DFS, rates of local and loco-regional recurrence, distant metastasis occurence, cosmetic outcome and QoL assessment. Acute and late toxicities will be scored according to the Common Terminology Criteria for Adverse Events (CTCAE) scale version 5.0 at each follow-up visit.

Regarding prospectively enrolled patient cosmetic assessment will be graded (by the physician and the patient) according to the Harvard scale and performed before the start of radiotherapy (RT), 6 months and 1, 2 and 5 years after the end of RT; frontal photographs of both breasts will be taken before the start of R, 6 months and 1, 2 and 5 years after the end of RT. In particular, two photographs will be taken of the patient's trunk region, one with the hands resting on the hips, the other with the arms raised above the head (avoiding patients face). Photographic documentation will be evaluated according to the consensus scoring method described by Haviland et al. For QoL assessment the EORTC (European Organisation for Research and Treatment of Cancer), QLQ-C30 and EORTC-QLQ-BR23 will be administered before the start of RT,1 month after the end of RT and then at 1, 2 and 5 years after the end of RT.

Follow-up visits are scheduled as follows: one month after the end of RT and then every 4-6 months for 5 years. Laboratory test (blood count, biochemical, with or without CEA and Ca15.3), mammography and breast ultrasound scans will be scheduled 4-6 months after the end of RT and then yearly. Additional exams will be prescribed during the follow up in order to detected any disease reccurence.

Inclusion Criteria:

• Female patients
• Age ≥ 18 years.
• Early stage breast cancer treated with breast conserving surgery
• Whole breast irradiation without regional nodal irradiation
• Infiltrating carcinomas
• CDIS
• Written informed consent

Exclusion Criteria:

• Age<18 years.
• Regional nodal radiotherapy.
• Distant metastases.
• Previous history of malignancy except basaloid skin tumours and CIN. Previous history of breast cancer is not an exclusion criteria if treated with curative intent and if patient is disease free at least 5 years from diagnosis.
• Presence of absolute radiotherapy contraindications (pregnancy, inability to maintain the correct treatment position) and relative radiotherapy contraindications (connective tissue diseases including rheumatoid arthritis, scleroderma, systemic lupus erythematosus, dermatomyositis and vasculitis, especially if the disease is in an active phase)
• Patient's refusal to use data for research purposes.

Patients affected by early stage breast cancer (both invasive and ductal carcinoma in situ) receiving ultra-hypofractionated whole breast irradiation (with or without a tumor bed boost) after breast conserving surgery. Main exclusion critereria are mastectomy and regional nodal irradiation .Neoadjuvant and/or adjuvant systemic therapies are allowed.