Merkel Cell Carcinoma Preceding Renal Primary Amyloidosis: Coincidence or Causality?

Introduction: We present a rare association of Merkle Cell carcinoma and nephrotic syndrome. Case Description: 63-year-old female presented with new proteinuria and lower extremity swelling. She had recently taken 7 days of ibuprofen and amox/clav. She was initially started on furosemide, without improvement. Blood work revealed albumin of 2.3 g/dL and a 24h urine protein 4.35g. Her total cholesterol 449 mg/dL, LDL 319 mg/dL,triglycerides 274 mg/dL. One month prior, she was diagnosed with non-metastatic Merkel cell carcinoma of her right thigh. Further workup revealed normal complements, negative ANCA, negatuve ANA. Kappa and lambda free light chains ratio of 6. SPEP showed hypoalbuminemia. A kidney biopsy dmeonstrated lambda light chain amyloidosis. Bone marrow biopsy identified lambda light chain restricted plasma cell population. Fluorescence in situ hybridization was negative for t(11;14). She was referred to oncology and started on chemotherapy. Discussion: AL amyloidosis is characterized by the existence of a plasma cell clone in the bone marrow that secretes immunoglobulin light chains. Their deposition leads to variety of presentations, including nephrotic syndrome, restrictive cardiomyopathy, peripheral and autonomic neuropathy. Screening of end-organ involvement is crucial for early treatment due to severity of prognosis. AL amyloidosis is not infrequently related to hematologic malignancies, such as monoclonal gammopathy of undetermined significant and multiple myeloma. Merkel cell carcinoma is a rare and aggressive cutaneous malignancy that affects older adults with light skin, especially in sun-exposed areas. Hematologic malignancies have been reported as a risk factor for Merkel cell carcinoma, most commonly chronic lymphocytic leukemia, more rarely multiple myeloma. Interestingly, patients with a preceding hematologic malignancy have a higher chance of being affected in an area not exposed to sun, such as our patient. This highlights 1) the non-coincidental occurrence of AL amyloidosis and an atypical presentation of Merkle cell carcinoma and 2) the need to further understand common physiopathological pathways. The question whether patients with an atypical Merkle cell carcinoma benefit from screening for hematologic malignancies remains.