Does PD itself or treatments for it increase risk
of developing malignant melanoma?
Patients with Parkinson’s disease have long been thought to have a 2-to
4-fold higher risk of developing malignant melanoma (skin cancer) than the
general population. What scientists don’t know for certain is whether this
increased risk is due to Parkinson’s disease itself or to specific
treatments: levodopa (including levodopa/carbidopa, Sinemet, Sinemet-CR,
levodopa/carbidopa plus Comtan, or Stalevo), one of the oldest, and Azilect,
one of the newest.
Since the late 1970s, a warning has appeared in the prescribing literature
for levodopa regarding the risk of activating malignant melanoma. Case
reports suggested that levodopa has a causal relationship with this form of
skin cancer due to their shared dopamine biochemical pathway. Evaluations of
these reports, however, concluded that the occurrence of both Parkinson's
disease and melanoma is “coincidental rather than causal.”(4) Patients on levodopa therapy did not appear to be predisposed to melanoma, nor did
levodopa therapy appear to exacerbate melanoma if it were previously
present.(4) In fact, levodopa has an “anti-tumor effect” on melanoma and
can be used safely in PD patients with a history of melanoma.(5)
New Danish research findings appear to further “weaken the hypothesis that
levodopa is causally related to an increased risk of malignant melanoma” in
people with Parkinson’s disease.(2) Doctors from the Institute of Cancer
Epidemiology in Copenhagen “examined the prevalence of malignant melanoma,
skin carcinoma, and other cancers before a first hospitalization or
outpatient visit for Parkinson's disease.”(2
The analysis compared the cancer histories of 8,090 patients with
Parkinson's disease to those of 32,320 randomly selected controls.
Participants eventually diagnosed with Parkinson's disease had a slightly
higher prevalence of cancer at any site compared to controls. The incidence
of malignant melanoma and skin carcinoma, however, was 44% and 26 % higher
respectively in patients with Parkinson's disease compared with controls.(2)
Verdict still out on Azilect and skin cancer
A small number of patients taking Azilect during the drug’s development
program were diagnosed with melanoma. The higher incidence of this form of
skin cancer is comparable to the increased risk observed in people with
Parkinson’s disease compared with rates in age- and sex- matched populations
from two epidemiologic databases.(1)
The FDA has concluded that the available data do not link Azilect to an
increased risk for melanoma. To definitively address this issue, the drug's
manufacturer will perform a phase IV (post-market) study. In the interim,
product labeling will recommend that patients undergo periodic dermatologic
examinations to monitor for melanomas.(1)/p>
Sources
(1) Miranda Hitti "FDA Approves Parkinson’s Disease Drug" WebMD Medical News
Reviewed By Louise Chang, MD on May 18, 2006 http://www.medicinenet.com/script/main/art.asp?articlekey=62083
(2) Reuter’s Health Information "Melanoma often seen before Parkinson's
disease" Medline Plus September 26, 2006 http://www.nlm.nih.gov/medlineplus/news/fullstory_39148.html
(3) Siple JF, Schneider DC, Wanlass WA, Rosenblatt BK. "Levodopa therapy and
the risk of malignant melanoma" Annals Pharmacotherapy (2000) 34: 382- 385
(4) Fiala KH, Whetteckey J, Manyam BV "Malignant melanoma and levodopa in
Parkinson's disease: causality or coincidence?" Parkinsonism & Related
Disorders (2003): 9: 321 - 327
(5) Weiner WJ, Singer C, Sanchez-Ramos JR, Goldenberg JN. "Levodopa,
melanoma, and Parkinson's disease." Neurology (1993) 43: 674 - 677
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