Complete Spontaneous Regression of Merkel Cell Carcinoma After Biopsy: A Case Report and Review of the Literature.

Merkel cell carcinoma (MCC) is a rare primary cutaneous neuroendocrine tumor that typically occurs on the head and neck of the elderly and follows an aggressive clinical course. Merkel cell polyomavirus (MCPyV) has been identified in up to 80% of cases and has been shown to participate in MCC tumorigenesis. Complete spontaneous regression of MCC has been rarely reported in the literature. We describe a case of a 79-year-old man that presented with a rapidly growing, 3-cm mass on the left jaw. An incisional biopsy revealed MCC. Additional health issues were discovered in the preoperative workup of this patient which delayed treatment. One month after the biopsy, the lesion showed clinical regression in the absence of treatment. Wide excision of the biopsy site with sentinel lymph node dissection revealed no evidence of MCC 2 months later. The tumor cells in the patient's biopsy specimen were negative for MCPyV by polymerase chain reaction and immunohistochemistry (CM2B4 antibody, Santa Cruz, CA). The exact mechanism for complete spontaneous regression in MCC is unknown. To our knowledge, only 2 previous studies evaluated the presence of MCPyV by polymerase chain reaction in MCC with spontaneous regression. Whether the presence or absence of MCPyV correlates with spontaneous regression warrants further investigation.

Mutually exclusive extracellular signal-regulated kinase pathway mutations are present in different stages of multi-focal pulmonary Langerhans cell histiocytosis supporting clonal nature of the disease.

AIMS: Pulmonary Langerhans cell histiocytosis (PLCH) is an idiopathic cigarette smoking-related disorder of the lung. Molecular changes in cellular or fibrotic stages of PLCH have not been investigated. We studied the prevalence of extracellular signal-regulated kinase (ERK) pathway mutations in different PLCH stages and other non-PLCH smoking-related lung diseases. METHODS AND RESULTS: The cohort included 28 PLCH with cellular (n = 10), mixed cellular/fibrotic (n = 4) and fibrotic histology (n = 14). Seven cases had concurrent multi-focal/multi-lobar tumours. Respiratory bronchiolitis interstitial lung disease (RB-ILD, n = 2), desquamative interstitial pneumonia (DIP, n = 4) and mixed RB-ILD/DIP (n = 2) were included for comparison. BRAF(V) (600E) immunohistochemistry, next-generation sequencing (NGS) and peptide nucleic acid (PNA) clamp polymerase chain reaction (PCR) with high analytical sensitivity (<0.1-0.2%) were used to analyse RAS, BRAF and MAP2K1 genes. Of 26 cases with gene mutation data, BRAF(V) (600E) was identified in eight of 12 (67%) cellular cases and in one of 14 (7%) fibrotic cases. MAP2K1 or KRAS mutations were observed in four of 14 (29%) fibrotic cases and three of the 12 (25%) cellular cases. Multi-focal/multi-lobar specimens carried identical BRAF (n = 5) or non-hotspot MAP2K1 (n = 2) mutations. The other smoking-related disorders were negative for mutations. Patients with cellular lesions or BRAF mutation were significantly younger than patients with fibrotic or BRAF wild-type PLCH. CONCLUSION: The presence of identical but mutually exclusive ERK pathway mutations in multi-focal PLCH supports a neoplastic/clonal origin for this disease. Patient age and mutation type differed between cellular and fibrotic histology and may indicate a natural progression or a mutation-specific pathogenicity.