# Post-Transplant Double Malignancy: Multiple Myeloma and Papillary Renal Cell Carcinoma—A Case Report

## TL;DR

A kidney transplant recipient developed two rare cancers, multiple myeloma and papillary renal cell carcinoma, highlighting the challenges of managing cancer while preserving the transplant.

## Contribution

This case report highlights the rare sequential occurrence of multiple myeloma and renal cell carcinoma in a kidney transplant recipient and evaluates treatment strategies.

## Key findings

- The patient achieved a very good partial response to VCd therapy while maintaining graft function.
- Progression of high-risk multiple myeloma on DKd was associated with significant infectious risks and a poor prognosis.
- Native-kidney papillary RCC was detected and surgically confirmed following initial myeloma treatment.

## Abstract

Background and Clinical Significance: Kidney transplant recipients have a 2–4-fold higher cancer risk than the general population. The sequential occurrence of multiple myeloma (MM) and native-kidney renal cell carcinoma (RCC) is rare and creates competing priorities between anti-myeloma efficacy and allograft preservation. Case Presentation: A 54-year-old woman with a 2020 living-donor kidney transplant presented in 2024 with bone pain and shoulder swelling. Low-dose whole-body CT showed multiple punched-out osteolytic lesions. Work-up revealed IgG-κ M-protein 38.5 g/L and 25% clonal plasma cells; cytogenetics showed a complex karyotype (R-ISS III). First-line bortezomib/cyclophosphamide/dexamethasone (VCd) was given while maintaining tacrolimus plus low-dose steroid. After four cycles, she achieved very good partial response (M-protein 42.3 to 5.6 g/L) with stable graft function. Follow-up imaging detected a large exophytic mass in the native right kidney; nephrectomy confirmed papillary RCC, type II. Later, the myeloma progressed with epidural extension causing cord compression. Second-line daratumumab/carfilzomib/dexamethasone (DKd) and palliative spine radiotherapy were initiated. The course was complicated by opportunistic infection and pancytopenia, and the patient died in January 2025. Conclusions: Vigilant post-transplant cancer surveillance—including native-kidney RCC—tailored immunosuppression, and multidisciplinary coordination are critical. VCd with tacrolimus may be feasible when graft preservation is prioritized; however, relapsed high-risk MM on DKd carries substantial infectious risk and a guarded prognosis.