Makoto Saito, Kencho Miyashita, Yosuke Miura, Reiki Ogasawara, Minoru Kanaya, Koh Izumiyama, Akio Mori, Takeshi Kondo, Masanori Tanaka, Masanobu Morioka, Shinya Tanaka

Colorectal follicular lymphoma (FL) occurs less frequently than duodenal-type FL, which is an established entity, and primary multiple FL only involving the colon is rare. Furthermore, the coexistence of lymphoma and multiple myeloma (MM) within the same patient is rare and the current study reports such a case. The patient was an asymptomatic 62-year-old man. He underwent colonoscopy screening, which revealed at least five polypoid tumors from the cecum to the rectum. Biopsy samples stained positive for CD20 and B-cell lymphoma 2 (BCL2) but stained negative for CD10, and fluorescence in situ hybridization analysis identified IGH/BCL2 in 95.2% of the tumor cells. Based on these findings, the patient was diagnosed with FL. On the bone marrow aspirate, the plasma cell count was 30% of all nucleated cells. Bence-Jones κ-type protein was detected by protein electrophoresis in serum and urine. The serum-free light chain κ/λ level was significantly elevated (484.3). Thus, the patient was also diagnosed with MM. Both FL and MM were targeted therapeutically; rituximab and bendamustine were effective for FL, and lenalidomide and low-dose dexamethasone were effective for MM. The patient was treated for 3 years and 7 months and, until now, was off-treatment for 4 years without rapid progression of the two malignancies. Although both diseases are still present, the patient has maintained stable disease. Our findings suggest that lymphoma and MM should be targeted separately as independent hematological malignancies when they occur concurrently.