Increased clarity on the use of radiotherapy in the management of desmoplastic melanoma

Desmoplastic melanoma (DM) represents a small (approximately 4%), but distinct subset of cutaneous malignant melanoma. As a consequence of its rarity, virtually all treatment information is gleaned from retrospective studies. Current recommendations regarding the use of adjuvant radiotherapy (XRT) in this disease are based on published data consisting of a relatively modest total number of patients. In this issue of Cancer, 2 large retrospective series focusing on the role of adjuvant external-beam XRT in the management of patients with DM are presented. Guadagnolo et al report their experience with 130 patients treated at The University of Texas MD Anderson Cancer Center (MDACC) and Strom et al present their data regarding 277 patients whose care was managed through Moffitt Cancer Center. At each institution, common treatment approaches were used, but essentially all final therapy decisions were made at the discretion of the individual physicians. Both groups reported prognostic factors for their entire patient populations, but also analyzed their data to identify the selected individuals who are most likely to benefit from adjuvant XRT or those who do not require it. The combined information contained in these 2 studies, which adds another 400 patients with DM to the published literature, helps to solidify treatment recommendations regarding adjuvant XRT and also points to areas remaining to be clarified. DM, which was first identified in 1971, was initially believed to behave more aggressively than other melanoma subtypes. In part, this sense derived from the finding that DMs were being diagnosed at a more advanced stage. The growth pattern and clinical appearance of DM can make them more difficult to detect, and therefore they often have progressed further than other melanomas before being identified as a malignant lesion requiring surgical resection. However, it does not appear to be the case that DM represents a more aggressive histology. The uncertainty regarding the clinical behavior of DMs was addressed in a matched-pair analysis comparing DMs with other cutaneous melanomas. This study demonstrated that, stage for stage and depth for depth, the 2 groups were similar with respect to overall survival. Although overall survival was comparable, there are extensive data demonstrating that the intrinsic biology of DM causes an increased propensity for local disease recurrence and a relative decrease in regional lymph node metastases. Initially, the relative importance of this aspect of their behavior may have been masked by their growth patterns, which often led to suboptimal resections resulting in inadequate surgical margins leading to a decrease in local control (LC). The pathologic classification system for DM is evolving and remains to be fully incorporated into overall management. Busam et al have identified 2 classes of DMs: “pure” and “mixed” based on the percentage of DM observed in a pathologic specimen (pure is> 90% vs mixed at> 10%, but< 90%). In studies separating out these 2 entities, the patients with pure DM demonstrated a characteristic biological behavior, compared with patients with mixed tumors, which generally behave more like the overall group of cutaneous melanomas. For example, in a study of lymph node involvement, Pawlik et al demonstrated that patients with pure DMs had a much lower incidence of positive sentinel lymph node biopsies (SLNBs) compared with patients with all other melanomas, whereas patients with mixed DMs had results similar to those of patients with other melanomas. In the studies under consideration, Strom et al had a pathologist re-review 64% of their samples with respect to these criteria, whereas Guadagnolo et al relied on the original pathology reports to put patients within the framework of the Busam classification system. DM is a malignancy presenting a predominantly local control issue and thus surgical resection and XRT are the basic elements of definitive treatment. With regard to the global question of whether patients with DM receive adjuvant XRT, the answer from both articles is: yes! If we consider the entire population of each study, the patients treated with