Case Report Highlights Rare Case of Tonsillar Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare neuroendocrine tumor that most commonly affects the head, neck, and trunk. However, a new case report highlights an extremely rare situation: tonsillar metastasis.

According to study authors, only about 100 cases of metastases to the palatine tonsil have been reported in scientific literature. Of those, only 5 reported cases have been metastatic MCC.

“Among the reported cases of metastatic MCC to the palatine tonsil, patients commonly presented with pharyngitis, dysphagia, and other oropharyngeal symptoms, years after wide excision of the primary cutaneous tumor,” they wrote in Clinical Case Reports.

The patient that is the subject of the new report was a 57-year-old woman who complained of a soft tissue mass in her right buttock that had been enlarging for 3 years. The mass measured 12 cm x 8 cm on physical examination, and so investigators performed a biopsy. The biopsy specimen was positive for cytokeratin 20, chromogranin, epithelial membrane antigen, and Merkel cell polyomavirus. It was negative for thyroid transcription factor-1 and cytokeratin 7. Based on those findings, the patient received a diagnosis of MCC. However, supplemental screening revealed something else.

“At our institution, fused fluorodeoxyglucose-18 positron emission tomography (PET)-CT scan noted asymmetric uptake involving the left tonsil region, concerning for neoplasm versus an inflammatory process,” the authors wrote.

The patient had not reported any symptoms in her tonsil area, and there was no palpable cervical or supraclavicular lymphadenopathy.

Surgery was planned, and physicians considered performing a preoperative tonsillar biopsy, but the patient’s care team decided against the procedure due to the risk of bleeding and sampling error. Instead, they followed consensus recommendations and removed the left tonsil and the right-buttock tumor. They also carried out a lymphadenectomy.

The patient was discharged after a 4-day inpatient stay and treated with a 1-year course of adjuvant avelumab (Bavencio) at a dose of 800 mg every 2 weeks. Over time, her Merkel cell polyomavirus titers decreased. As of the case report’s writing, the patient was 11 months out from her initial diagnosis without any evidence or progression.

The report authors concluded by discussing the rarity of this patient’s situation.

“Metastatic tonsillar tumors are uncommon due to the fact that the tonsil lacks afferent lymphatic vessels and histologically consists of mainly reticuloendothelial cells with strong ability to clear tumor,” they wrote.

The investigators said it is likely that the dissemination of the malignancy to the tonsil occurred via a hematogenous route.

They noted that the development of MCC is associated with Merkel cell polyomavirus in about 8 of 10 cases, and with chronic UV-mediated damage in the remaining 20% of cases. Patients with elevated Merkel cell polyomavirus oncoprotein antibody titers tend to have favorable outcomes, they said, “and when detectable, the oncoprotein antibody titer can serve as a tumor marker indicative of overall MCC burden.”

However, the investigators said Merkel cell polyomavirus status is not predictive of immunotherapy response. Instead, they said it is believed that efficacy is tied to tumor mutational burden.

“This current report is the first to present an asymptomatic, synchronous case of metastatic MCC to the tonsil,” they said. “Due to the natural history of this tumor, aggressive multimodal treatment is crucial.”

Reference

Okonkwo PC, Henning A, Plaza J, Agrawal A, Contreras CM. A rare tonsillar metastasis of Merkel cell carcinoma: a case report. Clin Case Rep. Published online March 19, 2023. doi:10.1002/ccr3.7063