Prostate cancer treatment with intensity-modulated radiation therapy (IMRT) is associated with a lower risk for second primary solid cancers compared with 3D conformal radiation therapy (CRT), investigators reported at the 2022 ASCO Annual Meeting.  

They based the finding on a retrospective cohort study of data from the Surveillance, Epidemiology and End Results (SEER) cancer registries and Medicare claims. The study included 45,811 men with nonmetastatic prostate cancer diagnosed at ages 66 to 84 years during 2002 to 2010. All men survived for 5 or more years after diagnosis without experiencing a second primary cancer. The men were followed until the earliest diagnosis of a second cancer, death, or December 2015. The median follow-up since prostate cancer diagnosis was 8.4 years.

“Our study suggests an overall reduced risk of developing a second primary solid cancer after prostate cancer IMRT vs CRT, which is consistent with better tumor targeting of the more advanced treatment method, IMRT,” investigator Kishan Pithadia, BS, of the National Cancer Institute in Bethesda, Maryland, said in an oral presentation. 

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A total of 2685 second solid malignancies were diagnosed during follow-up: 1380 in the CRT group and 1305 in the IMRT group. IMRT was significantly associated with a decreased risk for any second solid malignancy relative to CRT. Pithadia noted that “bladder and colon cancers did show a risk reduction with near-significant confidence bounds with the IMRT group.”

The investigators stratified patients by time since prostate cancer diagnosis (5.0-7.4, 7.5-9.9, and 10 or more years after diagnosis) to assess latency trends in developing second cancers. For all solid cancers and bladder cancer, they observed risk reductions that increased over time with IMRT compared with CRT.

Pithadia told attendees that “the most compelling pattern here for bladder and all solid cancers was a strengthening of the association with increased time since prostate cancer diagnosis. This is consistent with the latency patterns of radiation, as any association of second cancers with radiation is expected to be greater with longer follow-up.”

He concluded that the study found no clear association between IMRT and reduced risk for colon or rectal cancers compared with CRT.


Pithadia K, Advani PG, Schonfeld SJ, et al. Evaluating risk for second primary cancers by radiotherapy technique in prostate cancer survivors. Presented at: ASCO 2022; June 3-7, 2022. Abstract 12005.