DP21: Multidisciplinary management of Merkel cell carcinoma of lymph node without a skin primary: a case report with long-term follow-up

Myranda Attard,¹ Shyamal Raichura,¹ Damian McManus,² Joe Houghton² and Olivia Dolan¹

¹Dermatology Department and ²Institute of Pathology, Royal Victoria Hospital, Belfast Health and Social Care Trust, Belfast, UK

Merkel cell carcinomas (MCCs) are rare, high-grade neuroendocrine neoplasms. They pose a clinical challenge as there is only low-level evidence to guide management. A subgroup called MCC of lymph node without a skin primary (MCCWOP) are an even rarer occurrence that have demonstrated improved survival. We describe a case of MCCWOP managed and followed-up successfully for 7 years. A 62-year-old man presented with 4-week history of swelling in the right groin. There was no primary lesion on full-skin examination. Fine-needle aspiration followed by excision of the enlarged lymph node confirmed a diagnosis of intranodal MCC without extracapsular spread. Immunohistochemistry was positive for CAM 5·2, CK20, Synaptophysin and Bcl2, with weak staining for PAX5 and TdT. There was a high Ki67 labelling index of 80–90%. A baseline positron emission tomography showed no other foci of disease. The patient underwent right groin lymph node dissection and adjuvant radiotherapy to the right hemi-pelvis. All excised lymph nodes were negative for MCC. With the lack of established treatment guidelines for this rare diagnosis, specialist skin cancer multidisciplinary team meetings were fundamental at formulating a consensus management and follow-up plan. The recommended follow-up regimen mirrored that for high-risk melanoma. Six-monthly full-body computed tomography scans with contrast have been clear of local disease and distant metastases for 7 years. MCCs are aggressive tumours, with a relative mortality of 46%. Around 30% of cases will have metastasized at first presentation. Ten per cent of MCCs present as solely lymph node metastasis categorized as MCCWOP. It is unclear as to whether this diagnosis constitutes nodal metastasis with unknown primary or primary intranodal disease. The provenance of MCCs in 80% of cases is attributed to infection with polyomavirus, which becomes clonally integrated into MCCs, driving oncogenesis. The other 20% of MCC oncogenesis is driven by ultraviolet (UV)-mediated mutations. Reports of patients with MCCWOP testing polyomavirus negative but with UV signature mutations indicate that these nodal lesions possibly arise from primary skin disease. This would suggest that enhanced immune function may underlie the development of MCCWOP through elimination of the primary skin lesion. We present MCCWOP as a distinct entity with particular clinical behaviour and better survival than cutaneous MCC. This case adds to the limited body of evidence describing the management and monitoring of patients with MCCWOP. With a scarcity of guidelines and no precise staging system, there is a greater role for a multidisciplinary team approach to clinical management.