Immune therapy takes center stage
Another major transformation in MCC management has been the emergence of immune therapy as first-line systemic therapy. It has replaced chemotherapy, which is more toxic and has a much shorter average duration of response. Avelumab (Bavencio) and pembrolizumab (Keytruda), the two monoclonal antibodies directed against the protein programmed death–ligand 1 (PD-L1) receptor which are approved for MCC and have been incorporated into the National Comprehensive Cancer Network (NCCN) guidelines, provide a sixfold improvement in survival, compared with chemotherapy. For example, Dr. Nghiem was first author of a multicenter phase 2 study of pembrolizumab in which the 12- and 24-month overall survival rates in pembrolizumab responders were 85% and 79%, compared with just 12% and 6%, respectively, in historical controls on first-line chemotherapy (J Clin Oncol. 2019 Mar 20;37[9]:693-702).
“Merkel cell carcinoma is the most responsive solid tumor to immune therapy,” Dr. Nghiem commented.
Why MCC matters
Although rare, MCC is important because it’s five times more lethal than melanoma. Moreover, its incidence has been rising at a rate roughly twice that of the increase in melanoma since the turn of the century. There are now more than 3,000 new cases of MCC annually, about the same as for cutaneous T-cell lymphoma (CTCL).
“It’s just that you live a long time with CTCL and you don’t with Merkel cell carcinoma. You either get rid of Merkel fast or it gets rid of you,” the dermatologist observed.
It’s a fascinating malignancy, he continued. Eight of 10 cases are caused by Merkel cell polyomavirus, discovered in 2008. The virus is ubiquitously acquired in childhood and then lies dormant on the skin for the next 6 or 7 decades, at which point MCC rates shoot up dramatically, probably due to immunosenescence. Immunosuppressed patients are at 10-fold increased risk for MCC.
Given the rarity of MCC, it doesn’t make sense to actively hunt for it. But Dr. Nghiem and coworkers have developed a handy vowel-based mnemonic that serves to raise the index of suspicion: the “AEIOU” features.
- A = asymptomatic.
- E = expanding rapidly within past 3 months.
- I = immune-mediated.
- O = older than age 50.
- U = UV-exposed skin.
The investigators found in a series of 195 MCC patients that 89% of them possessed three or more of these features (J Am Acad Dermatol. 2008 Mar;58[3]:375-81). But while the AEIOU guide is quite sensitive, it’s not specific.
“If you have any three or more of these features, that lesion probably deserves a biopsy if it’s not readily explained. Even if it’s not a Merkel, it may turn out to be a different nonmelanoma skin cancer, something you want to know about,” Dr. Nghiem said.
A shift in surveillance strategy
Dr. Nghiem was senior author of a major study that validated the clinical utility of a Merkel polyomavirus serology test for monitoring the disease status of patients treated for MCC (Cancer. 2017 Apr 15;123[8]:1464-74). The test, which measures antibodies to Merkel cell polyomavirus oncoproteins, has been incorporated in NCCN guidelines. The blood test is used initially in newly diagnosed MCC to stratify patients into two subgroups: the half who are seropositive at baseline, and the other half who are seronegative. The seropositive group undergoes surveillance via repeat blood testing every 3 months. If antibody levels are low, there is a high degree of certainty that immune therapy is working and remission is present. Thus, the blood test spares patients in this group the expense and radiation exposure entailed in repeated surveillance scans. However, rising antibody levels indicate the cancer has already recurred or will do so within the next several months.