(PA-530) Second Primary Tumor in Patients with Multiple Myeloma in Brazil: A Population-Based Study

Introduction:  Multiple myeloma (MM) is a hematological malignancy derived from post-germinal center B cells that have differentiated into plasma cells. These neoplastic plasma cells proliferate clonally within the bone marrow and produce a monoclonal immunoglobulin (M protein) [1–4]. In 2022, approximately 188,000 new cases and 121,000 deaths due to MM were estimated worldwide [5]. Advances in treatment options have significantly increased five-year survival rates, consequently elevating the number of patients at risk of developing second primary tumors (SPTs) [6–9]. The aim is to evaluate the occurrence and characteristics of second primary tumors among patients diagnosed with MM in Brazil.

Methods:   A time-series study was conducted using data from Brazilian Population-Based Cancer Registries (PBCR), coordinated by INCA/MS, including MM cases (ICD-O-3 codes 9731/3 and 9732/3) diagnosed between 1991 and 2021. SPTs were defined as all malignant neoplasms diagnosed on the same date or after the MM diagnosis, excluding non-melanoma skin cancers (basal cell and squamous cell carcinomas). Sociodemographic variables (sex, age, race/skin color, education, occupation, and geographic region) and clinical data (tumor site and diagnosis date) were analyzed.

Results:   Among 12,255 MM cases identified, 2.7% (n = 340) developed an SPT. Most were male (53.2%), aged 60–69 (31.8%) or 70–79 years (30.9%). Regarding race, 49.1% were White and 29.7% Brown. The most common SPTs were prostate (23.5%), breast (15.2%), lower gastrointestinal tract (colon, rectum, anus; 8.2%), melanoma (7.6%), and extramedullary plasmacytoma (6.1%). Synchronous tumors were more frequent among younger patients: 55% occurred under 59 years old. Median age at diagnosis was 52 years for synchronous and 67–68 years for metachronous cases. Among synchronous tumors, extramedullary plasmacytoma accounted for 36%, followed by non-Hodgkin lymphoma, leukemia, breast cancer, and melanoma (each 9.1%). A decrease in SPT incidence was observed among women aged 40–59 years, from 0.40/100,000 (1991–2000) to 0.15/100,000 (2011–2021). Among men aged 60–69, incidence increased from 0.06/100,000 to 0.50/100,000 in the same periods. Breast (OR = 1.48; 95%CI: 0.67–3.39) and cervical cancers (OR = 1.80; 95%CI: 0.49–8.54) showed a higher chance of SPT among metachronous cases.

Conclusions:   In this national cohort of MM patients, the most frequent SPTs mirrored those of the general population (breast and prostate). However, synchronous tumors were more associated with rare hematologic neoplasms, particularly among younger individuals. Continuous surveillance for SPTs is recommended as part of MM patient care.