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Merkel Cell: It's Rare, Lethal, And Often Gets Misdiagnosed


 

OUR LUCAYA, BAHAMAS — Merkel cell carcinoma is more deadly than melanoma, and it is almost always misdiagnosed clinically, Dr. Henry W. Randle said at a meeting of the American Society for Mohs Surgery.

In a recent survey of 135 biopsy-confirmed Merkel cell carcinomas, 44% had been judged clinically to be cysts or acneiform lesions, 19% to be other nonmelanoma skin cancers, 9% to be dermatofibrosarcoma protuberans, and 28% received various other misdiagnoses. Just 2 of the 135 were accurately identified as Merkel cell carcinoma prior to biopsy. “Clinically, it's a problem. Almost no one identifies these up front. Keep it in mind in your differential,” said Dr. Randle of the Mayo Clinic in Jacksonville, Fla.

Indeed, Merkel cell carcinoma's clinical presentation is very nonspecific, consisting of firm, red to purple, nontender papules or nodules usually appearing on sun-damaged skin. Patients are typically over 65 years of age, with incidence about equal in men and women. Those who are severely immunosuppressed or who have undergone psoralen-ultraviolet-light (PUVA) treatment are at increased risk.

Although Merkel cell carcinoma is uncommon, its incidence tripled between 1986 and 2001, going from 0.15 per 100,000 age-adjusted population to 0.44/100,000 (J. Surg. Oncol. 2005;89:1–4). Absolute numbers are hard to obtain, but estimates range from 400 to 800 cases per year in the United States, he said.

Mortality is 25% within the first 3 years. However, patients who survive past 3 years are not likely to die of the disease. Survival is highly dependent on stage at diagnosis: Those with localized disease and lesions of less than 2 cm in diameter (stage 1) have a 90% survival rate at 3 years, whereas larger localized lesions (stage 2) reduce 3-year survival to 70%. Nodal disease (stage 3) reduces survival to just 30%, and metastatic disease (stage 4) kills 90%.

Sentinel lymph node biopsy (SLNB) should be performed routinely in these patients, because clinical examination is insufficient: In one study, 10 of 31 patients without palpable lymph nodes had a positive SLNB. Adjuvant treatment should be considered in all Merkel cell carcinoma patients with positive lymph nodes, Dr. Randle advised.

Treatment of the primary lesion involves either Mohs or wide (1–3 cm) excision. Dr. Randle tends not to use Mohs, however, because surgeons prefer to do both procedures at once rather than taking the node after the dermatologist has already operated on the cancer. “I usually send for wide excision and [SLNB], but you can use Mohs,” he noted.

Currently, radiation is the adjuvant treatment of choice for patients with positive sentinel nodes, while data on chemotherapy are less definitive. In one study, the addition of radiation to surgery, compared with surgery alone, resulted in lower rates of local recurrence (3% vs. 25%), nodal recurrence (22% vs. 42%), and distant spread (11% vs. 21%). “It's been questioned in the literature, but I think radiation clearly does help,” Dr. Randle remarked.

The risk for Merkel cell carcinoma is elevated 100-fold among individuals who have had PUVA treatment (N. Engl. J. Med. 1998;339:1247–8). For more information, visit www.merkelcell.org

The lesions tend to be nonspecific, consisting of firm, red to purple, nontender papules or nodules. Courtesy Dr. Henry W. Randle

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