Second malignancy probabilities for whole-pelvis RT vs. prostate only

Second malignancy probabilities in patients with prostate cancer treated with whole pelvis radiation therapy versus prostate only radiation therapy (2022)

"Abstract
Background
Whole pelvic radiation therapy (WPRT) may improve outcomes compared with prostate only radiation therapy (PORT) in some subsets of men with prostate cancer, as in the POP-RT trial. However, there is concern about increased risk of adverse effects with WPRT, including the development of radiation-induced second malignancies (SM). Given the rarity of SM, little is known about relative rates of SM between WPRT and PORT.

Methods
A retrospective cohort analysis was performed of men with nonmetastatic, node-negative prostate cancer with at least 60 months of follow-up using a national database. SM probabilities were compared in men receiving either WPRT or PORT using multivariable logistic models adjusting for clinical and sociodemographic factors. Temporal sensitivity analyses stratified by year of diagnosis and length of follow-up were also conducted.

Results
Of 50,237 patients in the study, 39,338 (78.4%) received PORT, and 10,899 (21.7%) received WPRT. Median follow-up was 106.2 months (interquartile range 82.32–132.25). Crude probabilities of SM were 9.16% for WPRT and 8.88% for PORT. The adjusted odds ratio (AOR) for development of SM with PORT versus WPRT was 1.046 (95% confidence interval 0.968–1.130). Temporal sensitivity analyses by stratifying by year of diagnosis and follow-up length also did not demonstrate any significant difference in rates of SM between WPRT and PORT using AORs with WPRT as the referent.

Conclusions
Retrospective analysis of over 50,000 patients did not demonstrate an association between WPRT and an increased probability of SM compared to PORT. Given the findings of POP-RT, the use of WPRT may become widespread for certain subsets of men. Thus, our findings could help guide how we counsel patients deciding between WPRT and PORT and suggest the need for prospective assessment of SM risk with WPRT and PORT."
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This is good news with regard to second primary tumors. The toxicity (adverse events) question remains, as does the longer-term picture (say, 15-20 years) with regard to bowel and bladder cancer for those men who have WPRT at an early age.

Djin

Looking good, Redwing!

Djin

It's hard to know, of course, since in all these studies there is a non-zero incidence in men who haven't received prior radiation to the area. As an anecdotal story, at one visit, I asked my uro/surgeon, who's been practicing for some 25-odd years, about second primary tumors after primary RT for PCa, and he said he was fairly sure that this happened in two of all his patients (I don't remember if it was two bowel cancer or one bowel and one bladder).

Djin