Background: Rates of contralateral prophylactic mastectomy (CPM) have more than doubled in the past decade amongst breast cancer patients irrespective of inherited genetic predisposition related to high penetrance genes. Increasing numbers of women with unilateral breast cancer are opting for removal of both the affected ipsilateral and unaffected contralateral ‘normal’ breast even when suitable for breast conserving surgery. Reasons for requesting CPM include prevention of recurrence, peace of mind and moving on after breast cancer. Some women seek CPM as a delayed procedure but factors influencing this are poorly understood. Methods: A retrospective analysis examined patients undergoing CPM as either an immediate or delayed procedure with or without breast reconstruction (BR) at a single tertiary referral centre between January 2009 and December 2019. A cross-sectional survey was undertaken that was compiled and based on validated questionnaires and responses to defined statements generated using a 5-point Likert scale (1 = strongly disagree to 5 = strongly agree) with calculation of mean scores and standard deviation (SD). This questionnaire explored patient’s decision-making process in terms of timing of CPM and any BR and was supported by subjective free-text boxes to gauge qualitative and quantitative aspects of the patient-related decision-making process. Those patients who consented to participate were provided with access to an online questionnaire. Results: Amongst this cohort of 39 delayed CPM patients, there were 6 decliners and therefore questionnaires were issued to the remaining 33 patients. The response rate was 67% (22/33) and the most common reason for seeking delayed CPM was to allow completion of adjuvant treatment recommendations (including radiotherapy/chemotherapy) before surgery on the unaffected breast [mean score 2.91; SD 1.0]. This avoided risk of delay in commencement of adjuvant treatment consequent to potential complications of contralateral surgery (especially with BR). The second most important reason for choosing delayed CPM was unavailability of genetic test results at the time of therapeutic mastectomy [mean score 2.64; SD 1.4]. The third most common reason was a subsequent change in family history cancer history after their personal breast cancer diagnosis that often prompted genetic testing [mean score 2.55; SD 2.7]. Several patients cited a shorter recovery time as a strong reason for requesting delayed CPM. Conclusion: Factors determining delayed CPM are patient-driven and this accords with documented reasons for women seeking CPM in general. Patients tend to make decisions about CPM based on two main themes relating to either ‘fear’ of cancer or a desire to ‘take control’. Temporal factors are important in the context of a delayed procedure and relate to subsequent availability of genetic test results and changes in family history in relatives who were otherwise unaffected at the time of initial diagnosis. Completion of all cancer treatments prior to delayed CPM (with BR) can be advantageous when implant-based BR is planned at the time of an immediate CPM. Radiotherapy can increase capsular contracture rates and surgical complications can delay start of chemotherapy. CPM should be offered as a potentially delayed option with informed discussion of risks and benefits. Citation Format: Chien Lin Soh, Samantha Muktar, Charles M Malata, John R Benson. REASONS FOR CHOOSING DELAYED RATHER THAN IMMEDIATE CONTRALATERAL PROPHYLACTIC MASTECTOMY IN PATIENTS WITH UNILATERAL BREAST CANCER. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-05-44.

Background: Challenges for breast reconstruction (BR) after delayed CPM relate to previous ipsilateral reconstructive procedures, adjuvant therapies and co-morbidities. The same type of BR for both sides may be impossible and use of an abdominal flap-based reconstruction for the therapeutic side precludes a similar technique for the contralateral side; an implant-based reconstruction may be difficult to size match with autologous tissue reconstruction. Alternative sites for tissue harvest are the latissimus dorsi and gluteal artery perforator flaps but these can be associated with significant donor site morbidity and poorer breast symmetry. Types of reconstruction and complications were evaluated in the context of BR and delayed CPM. Methods: A retrospective analysis examined breast cancer patients undergoing CPM either as an immediate or delayed procedure with or without breast reconstruction (BR) between January 2009 and December 2019. Clinical information was extracted from a prospectively maintained database with collection of data on demographics, timing and type of surgery, previous adjuvant treatments and complications. Patients undergoing delayed CPM were categorized into 4 groups based on BR or no BR and its timing in relation to both CPM and therapeutic mastectomy. Complications were listed according to the Clavien-Dindo system (scale of 1 – 5) with major adverse events being wound infection requiring intravenous antibiotics or drainage and explantation. Despite small numbers, complications were compared for therapeutic and prophylactic mastectomy together with the type and timing of reconstruction. Results: A total of 39 CPM patients were analyzed with 12 (31%) undergoing immediate BR at the time of cognate mastectomy, 22 (56%) choosing bilateral BR simultaneously with delayed CPM, 3(8%) opted for bilateral delayed BR following delayed CPM whilst 2 (5%) had no reconstruction. The mean patient age was 52 years (24–73) and the average interval between initial and delayed mastectomy was 2.67 years (0–22). The majority of reconstructions (28/39) were implant-based (72%) rather than exclusively autologous reconstruction and most patients had a similar type of BR for contralateral and ipsilateral sides. More than half of patients received neoadjuvant therapy and 85% had post-mastectomy radiotherapy prior to CPM. Major complications occurred in 8 patients (67%) with unilateral BR compared with 5 patients (23%) with bilateral immediate BR and 3 patients (100%) undergoing bilateral delayed BR. Small numbers and confounding factors preclude any robust statistical analysis but no statistically significant differences between the immediate and delayed BR groups were found on Fisher’s exact test. Complication rates appeared higher when immediate BR was performed after delayed CPM compared with therapeutic mastectomy. Conclusion: Potential complications and limitations of BR in the context of delayed CPM should be discussed with patients and used to inform decision-making processes for timing of CPM and associated reconstruction. There are no clear differences in rates of complications depending on laterality, type or timing of reconstruction. This study provides reassurance that reconstruction can be successfully performed either at the same time as delayed CPM (with or without BR on therapeutic side) or as a delayed procedure. Citation Format: Chien Lin Soh, Samantha Muktar, Charles M Malata, John R Benson. SURGICAL OUTCOMES FOR RECONSTRUCTION AFTER DELAYED CONTRALATERAL PROPHYLACTIC MASTECTOMY. [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-05-06.