Microscopic satellites around a primary melanoma: another piece of the puzzle in melanoma staging

This is an important subject that is applicable to surgical treatments of the primary melanoma and the regional lymph nodes as well as melanoma prognosis and staging. The importance of cancer staging, of course, is to partition patients into risk groups based upon disease-specific survival rates. In turn, the converse of survival rates at 5 or 10 years reflects the incidence of distant microscopic metastases at the time of staging from which a patient would ultimately succumb. With respect to the nodal (N) classification in melanoma, the two most important prognostic features are number of nodal metastases (1 versus 2/ 3 versus C4) and tumor burden (i.e., microscopic or clinically occult versus macroscopic or clinically apparent nodal metastases). The third criterion for defining the N category is the presence or absence of satellites or in transit metastases, regardless of the number of lesions. The clinical presence of satellites around a primary melanoma or of in-transit metastases between the primary melanoma site and the regional lymph node basin represent intralymphatic metastases that portend a relatively poor prognosis. The available data show no substantial difference in survival outcome for these two anatomically defined entities. But what about microscopic satellites? These are defined as any discontinuous nest of intralymphatic metastatic cells [0.05 mm in diameter that are clearly separated by normal dermis (not fibrosis or inflammation) from the main invasive component of melanoma by a distance of at least 0.3 mm. In the past, the definition of microsatellites has varied, and this may account for some of the differences in results regarding their prognostic significance. As a result, the level of evidence regarding the prognostic significance of microsatellites is less robust, but the available data indicates that this is an adverse finding associated with an increased risk of regional recurrences and a decreased disease-free survival rate similar to that of clinically detectable satellites. Whether microsatellites represent an independent predictor of survival outcome is less clear, but at present the preponderance of evidence suggests that this feature represents an adverse prognostic factor for survival. Accordingly, the America Joint Committee on Cancer (AJCC) Melanoma Staging Committee has recommended that this feature of early lymphatic metastases, as defined above, be retained in the category of N2c melanoma. This issue of the Annals of Surgical Oncology includes a valuable contribution to our decade-long work on melanoma staging as regards microsatellites. In this setting, the AJCC Melanoma Staging Database did not have direct data that could be applied to the staging rules for patients with microscopic satellitosis, except that published in the literature, much of which was published years ago. This study by Kimsey and colleagues from Memorial Sloan– Kettering Cancer Center (MSKCC) was made possible by the commitment made through the years by MSKCC surgeons to collect prospective data on their melanoma patients, which now includes almost 4,000 prospectively followed patients. Among these patients was a carefully studied cohort of 38 patients with newly diagnosed, clinically localized melanoma containing microscopic satellitosis. These primary melanomas had very aggressive features, including a median thickness of 5.4 mm and the majority (71%) being ulcerated. The 5-year overall and disease-free survival rates in these patients were 34% and 18%, respectively, and 68% had pathologically involved regional nodal metastases. They clearly constitute a highrisk group of patients for both regional and distant metastases that needs to be accounted for in our staging rules. In the 6th edition of the Cancer Staging Manual, the Melanoma Staging Committee modified its staging criteria Society of Surgical Oncology 2009