Before 2000, melanoma cases like Robert’s – those that didn’t show up on the outside of the skin – generally were considered to be metastatic melanomas of unknown primary origin. Now, melanoma specialists recognize a subtype they call “primary dermal melanoma” (PDM). There’s not much recent information available on  the web about PDM – here’s my synopsis of what’s there.

Primary dermal melanoma cases have some common threads:

·        there was no evidence of melanoma or abnormal pigmentation on the outer layer of the skin;

·        clinical tests, including skin examinations with ultraviolet light, PET/CT scans, and sentinel node biopsies, found no evidence of melanoma elsewhere on/in the body;

·        the lesions tended to be very deep; and

·        patients whose cancers were characterized as PDM had “remarkably prolonged survival” compared with metastatic or nodular melanomas of similar thickness.

That last bit sounds good to me! But apparently, not all melanoma cases with the first three characteristics noted above fall into that category.

The first report I found on a group of patients with melanomas not evident on the outer skin layer that did not appear to come from another site (i.e., metastasize) covered 11 patients. University of Michigan researchers reporting on this group in 2000 postulated that these cases were not metastases of melanomas of unknown primary origin, dubbed them “primary dermal melanoma,” and noted that they had an unusually high survival rate.

Another group, seven patients, classified as having PDM was reported in 2004 in an article by Dr. Susan Swetter (et al.) of Stanford University. This article noted that, under staging guidelines then in use, these cases would be considered Stage IV, metastatic melanomas of unknown primary origin. Other patients at that stage had a five-year survival rate of 19%, but the seven PDM patients then being followed at Stanford were all alive after up to five years of follow-up (mean, 41 months), which the report characterized as “markedly better than what would be expected” for a primary melanoma that deep or for a metastatic melanoma of unknown primary origin.

By 2008, the Stanford study cohort had grown to 13 cases. In these cases the mean thickness of the melanoma was 9.6 mm – about the same as Robert’s, 9.5 mm, which Dr. Sharfman has told us makes Robert’s case “high-risk.” Although the survival rate for PDM had begun to come down by then, it was still unusually high at 92% after a mean follow-up duration of 44 months.

The Stanford researchers’ 2008 report noted that they had found lower levels of staining for some proteins than they found in metastatic and nodular melanoma. This shows that the body of information about PDM had grown by 2008 to the point where some researchers believed they had found some markers for it in their immunohistochemistry studies. That’s why we were happy to hear that the team at Washington Hospital Center had Robert’s slides sent to Stanford for comparison with their identified cases. No answer yet – but we will follow up with Drs. Jang and Venna soon.

Even without knowing those results, we have reason for optimism. The importance of measuring the thickness (depth) of melanomas was highlighted in a 2009 World Journal of Surgery article reporting that 65% of patients with melanomas that were thicker than 4 mm had lymph node involvement. The researchers, from the Netherlands, said that finding a positive sentinel node was the only predictor of overall survival in patients with thick melanomas. Since Robert’s very thick melanoma was not accompanied by lymph node involvement, we hope that bodes well for his longer-term prognosis. 

We are taking what we can get right now - but continue to look for more information. We will consult with another top melanoma researcher, Dr. Lynn Schuchter, at the University of Pennsylvania next week. Stay tuned ... we'll keep you updated here!