Primary diffuse large B-cell lymphoma of the rectus abdominis muscle: a presumed primary case report and literature review.

Primary diffuse large B-cell lymphoma (DLBCL) of the skeletal muscle is an extremely rare subtype of extranodal non-Hodgkin lymphoma, and primary DLBCL of the rectus abdominis muscle is even rarer with few reports in the literature. Due to the lack of specific clinical manifestations and imaging features, it is easily misdiagnosed, leading to delayed treatment. We herein report an 85-year-old female patient who presented with a painful mass in the right lower abdominal wall. Preoperative contrast-enhanced computed tomography (CT) showed an irregular soft-tissue mass in the right abdominal wall with unclear boundaries abutting adjacent small-bowel loops. Tumour markers were within normal limits; complete blood count, lactate dehydrogenase, β2-microglobulin and peripheral-blood flow cytometry were unremarkable, and contrast-enhanced CT of the chest and brain magnetic resonance imaging (MRI) revealed no other lesions. Tumour markers were within normal limits. Contrast-enhanced ultrasound suggested a hypervascular malignant lesion. The diagnosis of a presumed primary DLBCL of the rectus abdominis muscle (non-germinal centre B-cell-like subtype) was confirmed by ultrasound-guided needle biopsy and immunohistochemistry. The patient received 4 cycles of an attenuated R-THP-COP regimen (rituximab, pirarubicin [tetrahydropyranyl adriamycin, THP, substituted for doxorubicin to reduce cardiotoxicity], cyclophosphamide, vincristine and prednisone). Partial response was achieved after 2 cycles, and complete radiological response on contrast-enhanced CT was obtained after 4 cycles. The patient remained free of reported abdominal symptoms during telephone follow-up (no further imaging surveillance was performed) and died of cerebral haemorrhage 3 years later, from a cause unrelated to the lymphoma. Primary muscular DLBCL is highly aggressive and easily misdiagnosed. Pathological biopsy combined with immunohistochemistry is the gold standard for diagnosis. In this single elderly patient, an attenuated R-THP-COP regimen was well tolerated and produced a sustained complete clinical response, suggesting that an individualised, biopsy-guided, chemotherapy-based approach may be a reasonable option for similarly localised disease in elderly patients; this observation, however, requires confirmation in larger series. This case enriches the clinical data of this rare disease and provides a reference for clinical diagnosis and treatment.