Evidence in real-world settings for multiple primary malignancies in prostate cancer: Comparison with single primary prostate cancers.

e23282 Background: With an ageing population and the improvement in prostate cancer survival, the diagnosis of Multiple Primary Malignancies (MPMs) involving prostate cancer has substantially increased, drawing greater focus in clinical practice. Patients under this condition pose a challenge for the sociosanitary system, as they require specific anticancer treatment strategies and cancer care. Cancer Registries (CRs) are postulated as enablers of evidence-driven care, shedding light on the theory-practice gap. The objective of this study was to address differences in real-world settings between patients diagnosed with prostate single primary tumors (SPT) and patients diagnosed with MPMs. Methods: Data of 2555 patients diagnosed with prostate cancer at a single institution from 2008 to 2018 was collected from the CR, 2431 (95,15%) diagnosed with SPT and 124 (4,85%) diagnosed with prostate as one of the MPMs. The classification of MPMs was done under the definition of the International Agency for Research on Cancer (IARC). Relapse-free survival (RFS), metastasis-free survival (MFS) and overall survival (OS) were estimated using the Kaplan-Meier method. A significance threshold of α < 0,05 was established. Results: In the overall population, median diagnosis age of 70 (Q1 65; Q3 74) years and a median PSA value of 8 (Q1 6; Q3 12) was observed. Tumors of stage II, differentiation grade of 2 and Gleason lower than 7 were the most common. Stage III tumors were more frequent on SPTs than on MPMs (p = 0,015), but no statistical difference is found regarding risk tumor categorization. Non-basocellular skin cancer, bladder, colon, rectum, bronchus and lung, kidney and stomach were among the most common other primary tumors. From the 124 MPMs, 101 (81,45%) were classified as metachronous and 23 (18,55%) as synchronous. The 5-year OS was 89,58 (95% CI 88,21-90,79) for SPTs versus 74,76 (95% CI 66,23-81,43) for MPMs (p < 0,001). Significant difference in OS was observed for bladder (p = 0,047), colon (p = 0,004), kidney (p < 0,001), rectum (p = 0,044) and stomach (p = 0,017) combined with prostate MPMs over SPTs. MFS at 5 years was 95,33 (95% CI 94,34-96,15) for SPTs and 91,44 (95% CI 84,66-95,31) for MPMs (p = 0,044). Difference in MFS was statistically significant for colon-prostate (p = 0,002) and prostate-kidney (p < 0,001) MPMs over SPTs. The 5-year RFS was 80,33 (95% CI 78,57-81,96) for SPTs and 84,35 (95% CI 76,27-89,86) for MPMs (p = 0,3099). Conclusions: Patients diagnosed with MPMs show significantly worse outcomes than patients diagnosed with prostate SPT. However, no difference is found regarding prostate tumor risk classification. MPMs such as prostate-kidney and stomach-prostate tend to have lower MFS and OS rates. Further analysis on a higher sample is required to study significant long-term outcomes. CRs arise as a strong asset to bridge the evidence gap in the study of MPMs.