[PTHrP-producing diffuse large B-cell lymphoma presenting with hypercalcemia at diagnosis]

A 55-year-old man was referred to our hospital with weight loss, somnolence, and dysarthria. Laboratory tests revealed elevation of serum creatinine (2.17 mg/dl), serum corrected calcium (16.3 mg/dl), and parathyroid hormone-related protein (PTHrP, 3.7 pmol/l). ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) demonstrated splenomegaly and increased FDG uptake in the spleen and in bone marrow throughout the body. Bone marrow biopsy showed infiltration of large atypical lymphoid cells. The neoplastic cells were positive for CD20, BCL-6, MUM1, PTHrP, and PTH1 receptor on immunohistochemical staining, prompting a diagnosis of PTHrP-producing diffuse large B-cell lymphoma (DLBCL). After one cycle of R-CHOP chemotherapy, the PTHrP level became undetectable; after four cycles, a complete metabolic response was confirmed on PET/CT. The patient subsequently underwent autologous peripheral blood stem cell transplantation and achieved long-term complete remission. PTHrP-producing DLBCL is extremely rare, and further investigation is needed to better understand its disease characteristics and pathophysiology.