A Systematic Review of Occult Malignancy and Sentinel Lymph Node Metastasis at the Time of Contralateral Prophylactic Mastectomy.

Background: Occult malignancy (OM) identified in contralateral prophylactic mastectomy (CPM) presents a challenge for axillary management.

Methods: This meta-analysis identified retrospective studies using PubMed, Embase, and Cochrane Reviews with the keywords OM and CPM. In this study, OM was defined as invasive disease only. To determine the proportion of OM and node positivity rates, MedCalc software was used.

Results: The 27 studies in this meta-analysis included 5728 patients who underwent CPM, with OM identified in 87 patients. The pooled incidence of OM was 1.55%. Of the 73 patients with axillary staging details available, 41 patients with OM (56%) underwent surgical axillary staging. Of these 41 patients, 8 had a positive sentinel lymph node (SLN) (20%), and 4 of the 8 patients had subsequent axillary lymph node dissection (ALND) with no additional positive lymph nodes identified. For 64 of the 87 patients with OM, T category was available. Of these 64 patients, 62 (97%) had pT1 and 2 (3%) had pT2 carcinoma. Histologic subtype was available for 52 OMs. Of these, 39 (75%) were ductal, 8 (15%) were lobular, and 5 (10%) were other. Biomarkers were available for 33 OMs, of which 21 (64%) were luminal A, 3 (9%) were luminal B, 3 (9%) were luminal human epidermal growth factor receptor 2 (HER2), and 6 (18%) were triple-negative.

Conclusions: Occult malignancy in CPM is uncommon (1.55%), and when it occurs, it is predominantly pT1, luminal A, or invasive ductal carcinoma. Occult malignancy with SLN metastasis occurs in only 0.1% of CPMs, and when present, SLN metastasis is low volume (≤2 nodes). This supports the current guideline recommendations against routine SLN surgery at the time of CPM.