Despite the popularity and proved safety of prepectoral implant-based reconstruction, there is little evidence on long-term results and variables which could influence surgical outcome. So far, no specific guidelines or indications have been developed for prepectoral technique and heterogeneous inclusion criteria had been used in previous reports. There is a lack of studies documenting outcomes following ADM-assisted prepectoral breast reconstruction, and there are no randomised controlled trial studies that drawing a direct comparison of clinical or patient-reported outcomes between subpectoral and prepectoral groups.

The investigators hypothesized that immediate acellular dermal matrix-assisted implant-based breast reconstruction with prepectoral implant placement would result in less early postoperative pain but more reported implant rippling, requirement of more fat grafting and an equitable safety profile compared with ADM-assisted implant-based breast reconstruction with subpectoral implant placement.

The aim of this study is to evaluate the postsurgical pain, complications and patient-reported outcomes of prepectoral breast reconstruction versus subpectoral implant placement in immediate breast reconstruction.

The investigators will employ a single centre RCT with duration of two years (July 1, 2019 - June 30, 2021). Participant recruitment and enrolment will occur at the Women's Health Center for 1 year (July 1, 2019 to June 30, 2020), followed by one year (June 30, 2021) of follow-up data collection, data analyses and dissemination.

At the preoperative consultation, the surgeon will determine if the patient is eligible for implant-based immediate reconstruction, using the inclusion and exclusion criteria.

A total of 56 patients or 23 patients per arm will be recruited. Randomization will be accomplished using randomly permuted blocks, and the randomization list will be prepared by a biostatistician with no clinical involvement in this trial. Randomization will be stratified on the basis of center and laterality of reconstruction (i.e., unilateral versus bilateral reconstruction).

The allocation sequence will be concealed by placing each randomization assignment in a sequentially numbered, opaque, sealed envelope. Consecutive envelopes will be delivered to the operating room by the on-site research study assistant once the mastectomy is complete. To prevent subversion of the allocation sequence, envelopes will not be opened until the attending surgeon confirms the absence of significant mastectomy flap necrosis and the fact that the patient does not undergo a concurrent axillary lymph node dissection.

All patients will be blinded to their treatment arm. Once the treatment arm is revealed, the attending surgeon will advise the surgical team (surgical assistants and operating room nurses) the surgical plan. While the surgical team will be aware of the randomization code, the rest of the postoperative care team (including recovery room staff, day surgery nursing staff, and clinic staff during follow-up visit), outcome assessors, and data analysts will be kept blinded to the intervention performed.

Outcome measures:

At the baseline visit, following informed consent, demographic data (age, BMI, laterality and comorbidities) will be collected. The participant will then complete the following questionnaires: Pre-operative Breast-Q™: The Breast-Q™ Reconstruction Module is a validated PRO developed specifically for patients undergoing breast reconstruction. The questionnaire evaluates patient-reported satisfaction, psychosocial, physical and sexual quality of life [1] Primary outcome: Postoperative Pain scores and 24-hour narcotic consumption Secondary outcomes: All outcomes are measured within or at 12 months of the initial surgery.

Inclusion Criteria:

• Female patient
• Ages 20-80
• All patients undergoing mastectomy for breast cancer or prophylaxis for breast cancer with immediate implant-based reconstruction
• Able to provide informed consent

Exclusion Criteria:

• Patients who have had prior chest wall or irradiation on the reconstructed side
• Patients not undergoing immediate breast reconstruction at the time of mastectomy
• Any patient with a contraindication to immediate breast reconstruction.
• Patients with history of smoking, BMI> 40, and D cup breast size or grade III ptosis are all contraindications to immediate breast reconstruction as the risk of postoperative complications are significantly higher (wound infection, dehiscence, implant loss, seroma) than the average patient and thus these patients would be excluded from the study.