Accuracy of PET-CT to Assess the Extent of Nodal Disease in Patients with Clinical Stage III Melanoma Following Neoadjuvant Treatment.

Background: Clinical stage III melanoma has a high recurrence rate following surgical dissection. The use of neoadjuvant treatment has been shown to improve long-term outcomes when compared with up-front surgery, with the pathological response being the best predictor. Biomarkers predicting responses and possibly allowing surgical de-escalation are missing. We aimed at assessing the correlation between post-treatment positron emission tomography-computed tomography (PET-CT) results and the pathological and long-term outcomes in a cohort of patients treated with a variety of regimens.

Patients And Methods: With IRB approval, we collected data on all patients with stage III melanoma treated with neoadjuvant intent at our institution since 2011 and assessed the association between their baseline features, post-treatment PET-CT findings, surgical pathological findings, and long-term outcomes.

Results: In total, 60 patients were identified; the median age was 61 years and 50% were males. The most common regimens used were immunotherapy (IO) in 42% and IO combined with targeted therapy (TT) in 48%. The imaging and pathological response rates were correlated at 60% and 65%, respectively. Both imaging and pathological response rates were higher for those treated with IO+TT than those with IO only, yet the presence of a major pathological response was predictive of a decreased risk of recurrence only in patients treated with IO. Overall, 67% had discordance in the number of involved lymph nodes between the PET-CT and pathological findings. PET-CT underestimation of lymph node involvement was associated with recurrence in those treated with IO only.

Conclusions: Post-neoadjuvant PET-CT findings should be interpreted with caution when considering the extent of the surgical dissection.