Abstract
Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine malignancy with an increasing incidence. Here we describe a case of a 72-year-old male who presented with a lesion of 5-6 months duration on his left elbow that was clinically thought to be a ganglion cyst. Histology revealed a Stage IIA Merkel cell carcinoma, with very scant cytoplasm, round to oval or polygonal hyperchromatic nuclei with dispersed chromatin and inconspicuous nucleoli. There were also numerous mitotic figures, apoptotic bodies and lymphovascular invasion. Anti-CK20 demonstrated classical perinuclear dot-like positivity. The patient underwent wide local excision and sentinel lymph node (SLN) biopsy with negative margins and negative SLN. Prior to the re-excision the patient did not receive chemo- or targeted therapy. The interesting finding in this case was that the excision specimen revealed only amphophilic, feathery deposits seen streaming throughout the process which demonstrated apple-green birefringence with Congo-Red stain, without any carcinoma cells. Amyloid deposition in Merkel cell carcinomas has been described in the literature in rare case reports, the last of which was published in 1982. Being a feature frequently been described in neuroendocrine tumors, amyloid change is not a surprising attribute to also be found in Merkel cell carcinoma. However, in extraordinary situations, as was the case for our current patient, the resection specimen may only show amyloid associated with a granulomatous reaction, with no viable tumor. Thus, it is important for practicing pathologists to be able to recognize that residual amyloid deposition may be evidence of a prior malignancy at that site (e.g., Merkel cell carcinoma). More vigilant and careful evaluation for residual tumor may be indicated.
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