Primary Parotid Non-Hodgkin's B-Cell Lymphoma in an Elderly Woman on Pembrolizumab for Metastatic Invasive Papillary Urothelial Cell Carcinoma of the Bladder.

Primary lymphomas of the parotid are rare (4-5%) and seldom appear in patients with pre-existing metastatic cancer from other primary sources. We present a primary marginal zone B-cell lymphoma of the mucosaassociated lymphoid tissue (MALT) in an 84-year-old female with preexisting metastatic bladder cancer. A PET scan that identified positive pelvic/cervical lymphadenopathy and bilateral parotid masses. She underwent transurethral resection of a bladder tumor and started on pembrolizumab chemotherapy. After two years, the left parotid mass decreased in size but the right increased to 3.9cm. Right superficial parotidectomy diagnosed B-Cell Marginal zone lymphoma, staining positive for CD20, PAX5, and Bcl2. pembrolizumab was held and the patient was started on 4 weekly rituximab infusions. A PET scan done 3 months after completion of rituximab showed a good response to chemotherapy. This is the first reported case of a primary parotid gland lymphoma in a patient with active metastatic bladder cancer.