In stage IIIA melanoma, nodal tumor size could guide decision-making

Among patients with American Joint Committee on Cancer IIIA early-stage melanoma metastases, the presence of sentinel node (SN) tumor deposits of 0.3 mm or higher is associated with a greater risk of disease progression, and these individuals may be well served by adjuvant systemic therapy. It suggests that those with smaller tumor deposits can be managed in a similar way to AJCC IB patients who are SN negative.

Those are the conclusions from a new prospective analysis of melanoma patients drawn from nine high-volume cancer centers in Australia, Europe, and North America. It was published online in the Journal of Clinical Oncology.

Classification of stage III melanoma is difficult since it comprises a heterogeneous group of patients with divergent prognoses. That complexity has resulted in four subcategories of stage III, ranging from high-risk primaries with synchronous nodal metastases (IIID) to patients with early-stage primary tumors with low burden at the SN (IIIA). The latter patients have excellent prognoses, with close to 90% 5-year survival. In fact, they have a better survival rate than some stage II patients with SN-negative, high-risk primary tumors (AJCC IIB-IIC).

Recent phase 3 trials have produced standardized protocols for treating stage III patients with intermediate to high risk (IIIB-IIID), but there is little evidence for the best approach to treat stage IIIA.

To fill that gap, the researchers examined data from 3,607 patients with low-risk primaries, defined as AJCC pT1b-pT2a. About 11.3% were AJCC IIIA and the rest were AJCC IB with no SN tumors: They served as a comparison group. The median follow-up was 34 months.

The researchers conducted a survival analysis that identified 0.3 mm as the optimal size to stratify outcomes. Among those with SN tumors 0.3 mm or higher, 5-year disease-specific survival was 80.3%. For those with smaller tumors, the rate was 94.1% (hazard ratio, 1.26; P < .0001). For distant metastasis-free survival the rates were 72.4% and 92.1% (HR, 1.27; P < .0001). Survival rates were similar between AJCC IB and low-risk AJCC IIIA patients.

The researchers found no differences between the AJCC IB patients and low-risk (< 0.3 mm) AJCC IIIA patients.

Other factors were associated with the presence of high-risk SN tumor size, including male sex (chi-squared, 4.97; df, 1; P = .034), and mitotic rates higher than 1/mm² (chi-squared, 4.92; df, 1; P = .035), although only mitotic rate remained a statistically significant risk factor after multivariate analysis (HR, 1.59; P = .050).

Where extracapsular spread was present, the median maximum tumor deposit size was 3.0 mm versus 0.5 mm in the absence of ECS (Kruskal-Wallis; F, 17.78; df, 1; P < .0001). High-risk nodal disease trended towards an association with N2a stage nodal metastases, compared with N1a stage disease (22.6% vs. 13.8%; chi-squared, 4.31; df, 1; P = .052).

The results of the study suggest that guidelines from the National Comprehensive Cancer Network and The National Institute for Health and Care Excellence could be missing up to one-third of patients with stage IIIA disease with high risk of distance recurrence or death, who may benefit from adjuvant systemic therapy. “We suggest that early-stage, AJCC IIIA patients with micrometastases of maximum tumor dimension [of at least] 0.3 mm should be considered for adjuvant systemic therapy or enrollment into a clinical trial, whereas patients with micrometastases of maximum tumor dimension less than 0.3 mm can be managed in a similar fashion to their SN-negative, AJCC IB counterparts,” the authors wrote.

Eight coauthors reported various conflicts of interest with pharmaceutical companies; the other coauthors reported no conflicts of interest.