P163 | SECONDARY PRIMARY MALIGNANCIES IN PATIENTS AFFECTED BY NEWLY DIAGNOSED MULTIPLE MYELOMA TREATED WITH AUTOLOGOUS STEM-CELL TRANSPLANTATION WITH OR WITHOUT MAINTENANCE WITH IMMUNOMODULATORY AGENTS: A TEN-YEAR SINGLE-CENTER EXPERIENCE

Background: Secondary primary malignancies (SPM) in multiple myeloma (MM) patients aroused interest due to the prolonged survival granted by new treatments. An oncogenic effect may be hypothesized for alkylating agents and immunomodulatory drugs (iMIDs) administered in first-line therapy. Aims: we analized incidence and risk factors of SPMs in MM patients treated with doublets or triplets and single or double stem-cell transplantation (ASCT) followed or not by maintenance with immunomodulatory drugs in real-life clinical practice. Methods: we retrospectively collected clinical and survival data of newly diagnosed MM patients that underwent at least a single ASCT from January 2010 to December 2020 in our center, with a follow-up to August 2024. We collected patient features (sex, age, autoimmune disease, previous neoplasms and their treatment), MM characteristics (monoclonal component, stage, cytogenetics, bone involvement), first-line treatment (induction, mobilization, number of ASCTs, consolidament and maintenance) and compared them in patients with and without SPM. Results: 189 patients, 101 males and 88 females, with median age at diagnosis of 59 years (range 35-74). 33 patients had high-risk FISH cytogenetics. 13 patients needed more than 1 mobilization to reach adequate CD34+ harvest, 136 underwent single and 53 double ASCT. 107 patients started iMIDs maintenance (80 lenalidomide, 27 thalidomide). 33 patients developed SPM (17%), including 46% cutaneous non melanoma, 15% hematological and 9% breast cancers, with a median onset of 70 months (13-277) from the diagnosis of MM, 59 (5-148) from the first ASCT and 64 (24-118) after maintenance start. The cumulative incidence was 6% at 5 and 15% at 10 years from the diagnosis of MM. Overall survival (OS) without and with SPMs was respectively of 73% and 99% at 5, 59% and 95% at 10 years after diagnosis. There were no differences in patients characteristics at diagnosis. We found correlation between the dose of cyclophosphamide (CP) for mobilization in thalidomide-treated patients and higher incidence of SPMs (p = 0.02). Moreover, the duration of lenalidomide maintenance beyond two years in patients with iMIDs in induction correlated with higher incidence of SPMs (p = 0.02). Conclusions: The development of invasive solid cancers and oncohaematological diseases after ASCT was rare and did not have an outcome impact. CP in mobilization and lenalidomide maintenance beyond 2 years may increase SPMs incidence.