Diffuse large B-cell lymphoma involving the vagina and a pre-existing uterine leiomyoma.

Lymphomas involving the female genital tract are uncommon, and vaginal involvement is particularly rare. In addition, the involvement of a pre-existing uterine leiomyoma by lymphoma appears unusual. Herein, we report the case of a woman in her sixties who presented with abnormal genital bleeding. Pelvic magnetic resonance imaging revealed a newly developed submucosal mass in the posterior vaginal wall and a previously known posterior uterine wall leiomyoma containing a newly emerged area of marked restricted diffusion. Both lesions showed relatively homogeneous internal signal characteristics and similar diffusion restriction, suggesting a shared pathological process. As the imaging findings indicated a gynecologic malignant neoplasm requiring surgical management, the patient underwent a simple total hysterectomy, bilateral salpingo-oophorectomy, and excision of the vaginal wall mass. Histopathological examination revealed diffuse large B-cell lymphoma, a nongerminal center B-cell subtype, in the vaginal lesion, with morphologically identical lymphoma cells infiltrating the uterine leiomyoma. Postoperative fluorodeoxyglucose positron emission tomography showed no additional lesions or abnormal uptake elsewhere, and the patient was subsequently treated with polatuzumab vedotin, rituximab, cyclophosphamide, doxorubicin, and prednisone. This case underscores the importance of considering lymphoma in the differential diagnosis when a vaginal mass shows a submucosal location, marked diffusion restriction, and relative internal homogeneity because early biopsy may help distinguish this entity from surgically managed gynecologic malignancies and thereby guide appropriate treatment.