A Rare Case of Comorbidity Between Intravascular Large B-Cell Lymphoma and Small-Cell Lung Cancer.

We report the case of a 60-year-old male with a fever for two months and a skin rash for approximately one month prior to visiting his local doctor and subsequent admission to the hospital. Clinical findings included fever, weight loss, and night sweats. Computed tomography (CT) revealed an irregularly shaped mass bordering the upper lobe of the left lung and mediastinum, as well as hepatosplenomegaly. Suspecting lung cancer or malignant lymphoma, the patient was referred to our hospital for further evaluation. Positron emission tomography-computed tomography (PET/CT) revealed hepatosplenomegaly with accumulation of contrast agents in the liver, spleen, and bone marrow, as well as in a mass in the left upper lobe. A liver biopsy revealed atypical cells in the sinusoids, and immunohistochemical staining confirmed B-cell lymphoma. Chemotherapy was initiated immediately. PET/CT at the follow-up evaluation showed that the hepatosplenomegaly and bone marrow-related accumulation of contrast agents had resolved, but the accumulation of contrast agents in the mediastinal lymph nodes and the left upper lobe mass persisted, despite shrinkage. A bronchoscopy and mediastinal lymph node biopsy were performed. Histopathological examination revealed that the lung mass was most likely a small-cell carcinoma of the lung. Clinically, the malignant lymphoma was considered intravascular large B-cell lymphoma. As a result of appropriate treatment for both cancers, the patient's survival period improved.