A 39-year-old African American female with 20-year history of HIV infection and hypertension presented with complaints of abdominal pain and decreased urinary output of 2 weeks duration. She had sustained a mechanical fall 2 weeks prior to presentation and had taken ibuprofen for pain control. Initial evaluation revealed a serum creatinine 5.5 mg/dL. Her baseline serum creatinine 3 months prior to presentation was 0.91 mg/dL. Urinalysis showed 3+ proteinuria and microhematuria, without microscopic casts. Urine protein-to-creatinine ratio was > 10 g/g. CD4 count was 267/µL and HIV viral load by PCR revealed viremia with 1,220 copies/mL. She was compliant with antiretroviral therapy (ART) consisting of bictegravir, emtricitabine, and tenofovir alafenamide (Biktarvy), and lisinopril 10 mg daily for hypertension. Non-contrast computed tomography (CT) scan of the abdomen and pelvis showed mild bilateral hydronephrosis, marked diffuse irregular bladder wall thickening and ascites. Bladder cystoscopy revealed no evidence of ureteral obstruction but showed diffuse nodules throughout the bladder wall; multiple bladder biopsies were obtained. Given her renal insufficiency, tenofovir was stopped and ART was changed to renally adjusted dolutegravir, rilpivirine, and lamivudine. Serologic workup, including complement C3 and C4, antinuclear antibodies, hepatitis C antibody, hepatitis B surface antigen, anti-neutrophil cytoplasmic autoantibody (ANCA) titers, and anti-GBM antibody, were negative. Serum protein electrophoresis was consistent with acute inflammatory stress response, with no evidence for a monoclonal protein. However, serum free κ light chains were elevated at 1,988 mg/L, with serum free κ/λ ratio 36.4. Urine immunofixation revealed monoclonal free κ light chains. Attempted bone marrow biopsy was unsuccessful. Diagnostic paracentesis was negative for malignancy. Hemodialysis was initiated on hospital day 6 because of progressive renal failure and uremic symptoms. Bladder biopsy revealed high-grade plasmablastic lymphoma (). Histopathology showed large plasmablastic cells diffusely positive for CD138, MUM-1, and negative for PAX-5, CD20, BCL-6, and BCL-2. Cell proliferation marker Ki-67 approached 100%. Tumor cells were positive for EBER1. Additional immunostains revealed that the plasmablastic lymphoma cells were κ light chain-restricted and positive for CD56, CD10, and c-MYC. They were negative for λ light chain, CD30, and AE1/AE3. Diagnostic kidney biopsy, performed 9 days after presentation, revealed focal atypical κ-restricted tubular casts with diffuse acute tubular injury and 30% interstitial inflammation and edema, consistent with κ light chain cast nephropathy (). There was no evidence of glomerular disease by light microscopy, immunofluorescence, or electron microscopy. Chemotherapy was initiated 2 weeks after initial presentation with bortezomib and CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone). She received 1 dose of intrathecal methotrexate, cytarabine, and hydrocortisone followed by 3 doses of intrathecal methotrexate alone to prevent central nervous system (CNS) relapse, which is common in patients with HIV-associated lymphoma []. She was maintained on ART during this period and started on trimethoprim-sulfamethoxazole and acyclovir for opportunistic infection prophylaxis. Seven weeks after initial presentation, renal function recovered, and hemodialysis was discontinued. Eleven weeks after presentation, the patient achieved complete remission by imaging (PET). Her chemotherapeutic induction regimen was then switched to bortezomib with ifosfamide, carboplatin, and etoposide (ICE) as CHOP is considered insufficient treatment for PBL []. Six months after presentation, repeat bladder biopsy showed no evidence of PBL and additional testing including PET and bone marrow biopsy were negative confirming complete remission. Seven months after presentation, she underwent modified BEAM (BCNU, etoposide, cytarabine, melphalan) followed by autologous hematopoietic cell transplant. At last follow-up 8 months after autologous hematopoietic cell transplant, her renal function remains stable (creatinine 1.07 mg/dL) with minimal proteinuria (urine protein-to-creatinine ratio 0.36 g/g), normal plasma free light chains, and improved HIV viral load (364 copies/mL). She tolerated chemotherapy well, except for peripheral neuropathy and onychodystrophy which were attributed to her chemotherapy.