Merkel cell carcinoma management undergoes revolution
This story appears courtesy of MDedge News
EXPERT ANALYSIS FROM SDEF HAWAII DERMATOLOGY SEMINAR
LAHAINA, HAWAII – The treatment of Merkel cell carcinoma is rapidly becoming much less toxic and more effective – and dermatologists have a key role in making this happen, Paul Nghiem, MD, PhD, declared at the SDEF Hawaii Dermatology Seminar provided by Global Academy for Medical Education/Skin Disease Education Foundation.
That’s because dermatologists are typically the physicians who make the diagnosis of Merkel cell carcinoma (MCC), so they’re on the scene from the outset and well positioned to help direct early management of this particularly aggressive malignancy, explained Dr. Nghiem, professor and head of dermatology at the University of Washington, Seattle.
“The management of Merkel is pretty high stakes, and if you get it right at the beginning it makes a huge difference in the side effects, as well as the chances that the patient will have the disease under control,” said Dr. Nghiem, who is sometimes called “the Merkel man” because of his many pioneering contributions to the field.
Better early management
Getting early management right, he added, hinges upon ordering a baseline PET-CT scan to search for metastases before performing definitive surgical excision of the primary tumor.
“There are really important prognostic and therapeutic implications for a baseline scan in almost any patient with early Merkel – and that’s a very different situation than with melanoma,” the dermatologist said. “There’s at least a threefold higher likelihood that the cancer has spread asymptomatically at baseline with Merkel cell carcinoma than with melanoma.”
In a soon-to-be-published study by Dr. Nghiem and coworkers, baseline imaging resulted in prognostically important upstaging that led to an altered management strategy in 12% of 584 patients with MCC, or 1 in 8.
“You don’t want to overtreat locally a lesion that has already spread distantly; you want to start focusing on the distant disease. The local disease is secondary,” he said.
The surgical excision of the primary lesion should be thoughtfully wide without being aggressive or mutilating, and it should involve primary closure. “Definitely avoid flaps and grafts, which delay your further management with radiotherapy by months and months,” Dr. Nghiem advised.
Adjuvant radiotherapy of the primary tumor site is extremely effective at preventing recurrent MCC. In Dr. Nghiem’s view, almost everyone is a candidate: In a series of 803 patients in the Seattle MCC cohort, 92% received local adjuvant radiotherapy. The national rate, in contrast, is only about 50%, highlighting the need for additional physician education.
“A little bit of radiation – one dose – appears to be just as effective as 6 weeks in controlling microscopic disease. That’s probably something we’re going to be moving towards as a field,” he predicted.
Indeed, local adjuvant radiotherapy is so effective in MCC that the surgical margins make no difference. This was demonstrated in a study by Dr. Nghiem and his coinvestigators involving 70 patients with margins greater than 1 cm who received radiotherapy, 70 others with smaller or even positive margins who received radiotherapy, and 35 patients with margins of 1 cm or less who did not receive radiotherapy. There were no MCC recurrences in any of the radiotherapy recipients, regardless of their margin status. In contrast, 7 of the 35 patients who didn’t receive radiation therapy developed a cancer recurrence. Of note, the recurrence rate of MCC is historically about 40% – far greater than for any other skin cancer. Most recurrences happen within the first 2-3 years, Dr. Nghiem observed.
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;37:693-702).
“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;58:375-81). 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;123:1464-74). 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.
Unfortunately, the blood test cannot be used serially to track disease status in patients who are seronegative at baseline. That group is at 42% increased risk of MCC recurrence.
Immune therapy works in only about two-thirds of MCC patients with distant disease. Leaving the visible primary tumor in place to serve as a real-time window into immune treatment effectiveness is a useful contemporary surveillance strategy.
“By leaving the visible primary there, you will rapidly know if that patient is in the favorable two-thirds group or not,” he explained.
Historically, surgery and surveillance of MCC were based upon the melanoma model, and medical oncologists were trained to treat the malignancy as they would small cell lung cancer. These are now outmoded approaches, Dr. Nghiem said. That’s why a multidisciplinary approach is highly desirable for management of MCC, including dermatologists, pathologists, surgeons, radiation oncologists, medical oncologists, and imaging experts.
Dr. Nghiem and his colleagues have created a comprehensive source of information about Merkel cell carcinoma for physicians and patients at merkelcell.org.
He reported receiving research grants from Bristol-Myers Squibb and serving as a consultant to EMD Serono, Merck, Sanofi/Regeneron, and 4SC.
SDEF/Global Academy for Medical Education and this news organization are owned by the same parent company.
By Bruce Jancin