CHICAGO – , including those without palpable lymph nodes, according to results of an analysis of a large MCC registry presented at the annual meeting of the Society for Investigative Dermatology.
The results were a “surprise,” according to Neha Singh, a researcher in the division of dermatology at the University of Washington, Seattle. She contended that many treatment guidelines for MCC, including imaging at the time of diagnosis, are borrowed from those developed for melanoma but should not be.
“MCC is much more frequently metastatic to regional and distant sites than melanoma, so current melanoma guidelines may not be appropriate for use with MCC,” she said. According to the data she cited, 41% of MCC patients, versus 14% of melanoma patients, already have metastatic disease at the time of diagnosis.
The presence of more aggressive disease and the need for scanning was confirmed in the analysis of the MCC Registry in Seattle, which contains 1,439 patients. Of 586 patients who met inclusion criteria for this analysis, 493 MCC patients had no palpable lymph nodes at the time of diagnosis. Yet, 60 (12%) proved to already have regional or distant metastases on the basis of scans.
This contrasts starkly with melanoma data, according to Ms. Singh. Guidelines from the National Comprehensive Cancer Network (NCCN) do not recommend scans in melanoma patients without palpable lymph nodes based on evidence that only 1% of these will be upstaged by imaging. This figure was judged too small to justify routine scans, she said.
In melanoma patients with palpable lymph nodes, NCCN guidelines do recommend imaging at diagnosis because upstaging is common, and the same is true in MCC, Ms. Singh noted. In the Seattle registry, 10 (11%) of the 93 patients with palpable lymph nodes were upstaged for distant metastases found on imaging.
In those without palpable lymph nodes, “even a small tumor does not guarantee the absence of distant metastases,” Ms. Singh cautioned. Although the median tumor size in this group was 2.3 cm, tumors of less than 1 cm were still associated with distant disease.
The likelihood of distant disease in MCC patients without palpable lymph nodes might be even greater than that identified in this analysis. At least some of the patients in this series were evaluated with CT rather than PET imaging, which is more sensitive. Ms. Singh reported that no stratification to determine rates of distant disease by imaging type have yet been undertaken in this dataset.
Based on these findings, guidelines for MCC should include consideration of baseline imaging in all patients, Ms. Singh said. In making this point, she also emphasized the guidelines for melanoma should not be considered transferable to MCC.
“Why is this important?” Ms. Singh asked. Understaging MCC “may lead to inadequate surgery, overaggressive local therapy, and a potential delay to effective systemic therapy.”