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Intermediate Thickness Melanoma: A Population Based Study Of Surgical Quality Metrics
Mara A Piltin, *Amy Glasgow, *Elizabeth Habermann, Tina J Hieken
Mayo Clinic, Rochester, MN

Objective(s): Variability in guideline compliance for lymph node (LN) surgery for melanoma patients is attributed to controversy about patient selection. Prior data indicate suboptimal practice of sentinel LN biopsy (SLNB) and a trend toward omission of LN dissection (LND) for LN+ disease, well before MSLT-II trial data publication. To minimize bias, we studied compliance with ASCO/SSO guidelines among T2/T3 (intermediate-thickness) melanoma patients, where general agreement on the value of surgical nodal staging exists.

Methods: T2-T3, M0 melanoma cases were identified from 2004-2018 SEER data. Cancer specific survival (CSS) was estimated using the Kaplan-Meier method; Cochran-Armitage test for trends and multivariable logistic regression analyses were performed.

Results: Of 66,294 eligible T2/3 patients 57,212 were cN0, 1,839 cN+, 7,243 cN unknown (Table). Overall, 19,032 (28.7%) had no LN surgery. Among cN0 patients 41,427 (72.4%) underwent SLNB and 6,382 (15.4%) were pN+, whereas 1,160 cN+ patients (63.1%) had a LND and 426 (23.2%) had SLNB only. LND rates declined from 2004 to 2018, 79.8% to 32.0% for cN0/pN+ patients, and 72.5% to 59.2% for cN+/pN+ patients, both p<0.0001. Guideline compliance for LN surgery improved from 67.9% to 70.3% (2004 to 2018) for cN0 patients but worsened for cN+ patients (63.1% to 43.7%), both p<0.0001. In multivariable analysis, compliance correlated with younger age, male sex, and primary tumor mitotic rate and site (extremity>trunk/head/neck), p<0.0001. cN0 guideline-compliant versus non-compliant care carried a 5-year CSS of 90.0% versus 83.4%, p<0.0001.

Conclusions: Despite clear guidelines, one-third of intermediate-thickness melanoma patients in a recent cohort did not have recommended LN surgery. Adjuvant Stage III melanoma trials evaluated only patients treated with LND, but drug approvals were not conditional on LND although nodal burden is a key factor determining both the need for active surveillance of pN+/cN0 patients and the relative benefit of costly and potentially toxic adjuvant therapies. These data highlight a clinical care gap and suggest efforts to improve guideline compliance are a logical strategy to improve cancer outcomes for intermediate-thickness melanoma patients.

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