Melanoma Upstaging During Mohs Micrographic Surgery: A Single-Center 12-Year Experience.

BACKGROUND: Mohs micrographic surgery (MMS) with MART-1/Melan-A immunostaining is increasingly used for melanoma in situ and invasive melanoma. Permanent section analysis of the central debulking specimen can reveal previously unrecognized or deeper invasion, resulting in tumor upstaging, but the frequency and clinical yield of this practice remain unclear. OBJECTIVE: To determine the frequency of melanoma upstaging on debulking specimens and compare routine versus selective, frozen section-guided submission. MATERIALS AND METHODS: Single-center retrospective review of all cutaneous melanomas treated with MMS by one surgeon (2010-2022). Debulking specimens were submitted routinely (2010-2015) or selectively based on intraoperative frozen section features (2016-2022). The Fisher exact test was used to compare upstaging between eras. RESULTS: Among 2,017 melanomas (75.8% in situ), 36 (1.8%; 95% CI: 1.3%-2.5%) were upstaged, all by increased Breslow depth. Overall upstaging was 2.5% (routine) versus 1.5% (selective) (p = .138). In the selective era, debulking specimens were submitted in only 25 cases, of which 21 (84.0%) showed upstaging, reflecting strong concordance between intraoperative frozen section suspicion and permanent section findings. Most upstaged tumors were low risk (77.8% T1a-T1b); only 22.2% reached T2a or higher. CONCLUSION: Melanoma upstaging during MMS is uncommon and usually low risk, supporting a selective, individualized approach to permanent section submission guided by intraoperative frozen section findings.