Concordant clear cell “mesonephric” carcinoma of the bladder and lung adenocarcinoma with clear cell features – multiple primaries versus metastatic neoplasms: a case report

Background Clear cell carcinoma of the bladder is a rare variant of urinary bladder adenocarcinoma. We report a case of a patient with clear cell carcinoma of the bladder and a concordant right upper lobe pulmonary adenocarcinoma with clear cell features, and we address the role of immunohistochemistry and cytogenetic analysis in distinguishing the two primary malignancies. Case presentation Our patient was a 59-year-old African American woman who presented with hematuria. Her past medical history included invasive mammary carcinoma and end-stage renal disease treated with hemodialysis. A computed tomographic urogram revealed a 3-cm polypoid bladder mass. A follow-up chest computed tomographic scan revealed a 1-cm right upper lobe nodule. The patient underwent transurethral biopsy and subsequent radical cystectomy, as well as a transthoracic core needle biopsy of the lung nodule. Histologically, the bladder tumor consisted of flat, cuboidal to columnar cells with clear or eosinophilic cytoplasm and a hobnail appearance, organized in tubulocystic and papillary patterns. The neoplastic cells were diffusely positive for α-methylacyl-coenzyme A racemase, cancer antigen 125, and cytokeratin 7; focally positive for cytokeratin 20, P53, and carcinoembryonic antigen; and negative for thyroid transcription factor 1. The lung tumor demonstrated a glandular architecture with mucin production (positive for mucin with mucicarmine and periodic acid-Schiff with diastase stain). The neoplastic cells were diffusely positive for cytokeratin 7, napsin A, and thyroid transcription factor 1, and they were negative for cytokeratin 20 and cancer antigen 125. Genetic testing of the pulmonary neoplasm demonstrated ARID2 genomic alterations. Conclusions The presence of clear cell features in both neoplasms raised the possibility of lung metastasis from the primary bladder tumor. However, the glandular architecture of the lung neoplasm along with its distinctive immunohistochemical and genetic profiles confirmed the presence of two separate primaries.