Second Malignant Neoplasms (SMN) in Myeloma Patients Post Stem Cell Transplant (SCT)

Introduction: Recent developments in management of patients with myeloma have resulted in longer survival. Availability of newer class of agents for treatment has prolonged survival, improved quality of life and achieved better disease control. Use of SCT, either autologous (AutoSCT) and to a lesser extent allogeneic (AlloSCT) still forms an important aspect of myeloma treatment pathway. Improved survivorship mandates evaluation of long term consequences and risk of SMN is one of the most important long-term consequences affecting overall outcome.

Aim: Estimate the risk of SMN post SCT in patients with Myeloma.

Methods and Materials: Analysis includes 779 patients who received SCT for myeloma from January 2002 to December 2019. Data was collected using case records, electronic patient records, transplant database and information from referring hospitals. Follow-up was updated to June 2020.

Results: Analysis includes 779 patients with myeloma (M: 488, F:291; median age:59yr, range: 26-75) receiving AutoSCT (n=716) or AlloSCT (n=63). Conditioning for AutoSCT was high dose melphalan in majority (n=714, 99.7%). AlloSCT conditioning was RIC (n=40/63, 63.5%) or MAC (n=23/63, 36.5%). TBI was part of conditioning in 51/779 (6.5%). There was no difference in demographics between two groups.

Results: Median follow-up was 46 mo (range: 0.2-220). Second malignancy was identified in 48 of 779 cases (6.0%). SMN developed in 6/63 (10%) AlloSCT and 42/716 (6%) AutoSCT patents (p=0.25). SMN types were haematological (n=21), lymphoma (n=6) and solid tumours (n=21). MDS was the only haematological SMN in this series. Secondary MDS developed in 20/21 of AutoSCT as compared to 1/63 in AlloSCT (p=0.01). Non-haematological SMN were breast (n=3), upper GI (n=3), lower GI (n=2), hepato-billiary (n=2), prostate (n=3), skin (n=5), and unknown primary (n=1). SMN incidence was higher with increasing follow-up (2002-2014, 8%; 2015-2017, 2.8%, 2018-2019, 0%, p=0.002). There was no association with development of SMN and gender, age at transplant, type of stem cell source or transplant conditioning. Incidence of SMN was significantly higher for all sites as compared to general population. Cumulative incidence of SMN was 5% at 5 yr, and 15% at 10 yr for AutoSCT patients.

Conclusion: Myeloma patients are at increased risk of SMN and need monitoring for long term side effects. Development of MDS post AutoSCT is the commonest SMN post AutoSCT but there is increased incidence of solid tumours as well. Impact of new modalities of treatment needs long term monitoring.