All patients undergoing mastectomy for breast cancer should be offered the option of reconstructive surgery. The Deep Inferior Epigastric Perforator Flap or DIEP reconstruction as it is commonly referred to, is becoming the favoured reconstruction by both patients and surgeons as it gives a great cosmetic outcome as well as being a good option for patients who may have to undergo radiotherapy treatment after their surgery.

Exercise has been demonstrated in previous research to improve tolerance of treatment (particularly chemotherapy), post operative fatigue and the overall quality of life in patients undergoing cancer treatment. Furthermore, it has shown to improve survival in patients who are being treated for breast cancer. The investigators are undertaking this study to investigate whether a structured exercise programme will improve patients fitness after surgery and ultimately improve their recovery after their reconstructive surgery. To do this, half of the people taking part will be undertaking a structured exercise programme and the other half will not and will be assessing which group recover better after their surgery. Currently, no breast reconstruction patients in Ireland are receiving a formal "exercise prescription" after their surgery so will be looking to see if this helps people recover better before it is made standard care for every breast patient in Ireland.

Primary Objective:

To evaluate the impact of a structured, post-operative exercise programme on patient-reported and functional outcomes following DIEP flap breast reconstruction.

Secondary Objectives:

• To examine the effects of the exercise programme on upper and lower limb strength, body composition (BMI, fat and muscle mass, bone density), and functional recovery.
• To evaluate the influence of exercise on post-operative complication rates, length of hospital stay and time to return to daily activities.
• To explore changes in psychological health and body image perception using validated questionnaires.
• To assess adherence, feasibility, and safety of the structured exercise programme within a breast reconstruction population.
• To perform an exploratory health-economic analysis comparing the costs and potential healthcare savings associated with the intervention versus standard care.

Inclusion Criteria:

1. Women aged 18 years and older

2. Candidates who have already been selected to undergo mastectomy and reconstruction by the breast MDT for the following indications:

   1. Genetic mutation carriers undergoing risk-reducing mastectomy.
   2. Ductal carcinoma in situ (DCIS) requiring mastectomy.
   3. Early invasive breast cancer requiring mastectomy.
   4. The tumour must not have skin involvement and no evidence of invasive disease within 1cm of skin, nipple or pectoralis major muscle (as proven on MRI).

3. Candidates for breast reconstruction with DIEP.

4. Fluent in English

5. Fit for general anaesthetic Signed informed consent form

Exclusion Criteria:

1. Advanced breast cancer with skin involvement.
2. Undergoing bilateral DIEP reconstruction or other forms of breast reconstruction (e.g., TRAM, implant-based, LD flap).
3. Pregnancy
4. Lactation Patients with insufficient English to sign an informed consent (i.e. interpreter required).

This study is post DIEP breast reconstruction

Individual participant data will not be shared as this could potentially identify participants. Anonymous datasets will be available for validation.