# Rectal cancer following radiotherapy for prostate cancer: A propensity‐matched analysis

## TL;DR

Men who had prostate cancer radiation face a higher risk of developing rectal cancer later, which often requires more invasive surgery but has similar survival rates as primary rectal cancer.

## Contribution

This study provides the first detailed comparison of clinical features and outcomes of secondary rectal cancer after prostate cancer radiation versus primary rectal cancer.

## Key findings

- Secondary rectal cancer patients were older and had more comorbidities than primary rectal cancer patients.
- Secondary rectal cancer patients underwent more extensive surgeries and fewer sphincter-preserving procedures.
- Despite these differences, survival rates were similar between the two groups.

## Abstract

Patients who have previously received radiation therapy for primary prostate cancer (PPC) face an elevated risk of developing secondary rectal cancer (SRC). However, the clinical presentation, surgical outcomes, and oncological results of SRC in this context remain poorly characterized.

This study aims to compare the clinical and pathological features, as well as treatment outcomes, of patients with primary rectal cancer (PRC) and those with SRC following radiation for prostate cancer.

Retrospective cohort study using univariate and propensity‐matched analyses.

Data extracted from electronic medical records at a single tertiary institution [2001–2021].

Male patients with rectal cancer (RC) who underwent oncological resection with or without a prior history of prostate cancer radiation. Patients with a <3‐year interval between radiotherapy and RC diagnosis were excluded. The main outcome measures were pathological analysis, postoperative complications and overall survival.

Out of 1,755 patients with RC, 50 cases (2.9%) had SRC. Forty‐three out of the 50 patients were included in the analysis. The median time from radiotherapy to SRC diagnosis was 8 ± 4 years (IQR). Patients with SRC were older, with a mean age of 73.7 ± 8.5 versus 61.1 ± 13 years in the control group (p < 0.001), and a higher American Society of Anaesthesiologists (ASA) score (p = 0.006). Most SRCs were distal with a median distance from the anal verge of 4.25 cm (IQR 9.5 cm). Only seven patients (16.3%) in the SRC group received neoadjuvant radiation therapy versus 764 (44.8%) of PRC (p = 0.001). SRC patients required more extensive surgical interventions, including abdominoperineal resection (46.5% vs. 29.9%), pelvic exenteration (4.7% vs. 0.4%), and fewer sphincter‐preserving procedures, including low anterior resection (48.8% vs. 68.2%) and transanal resection (0% vs. 1.5%) (p = 0.02). Propensity score matching with a 1:2 ratio matching for age, body mass index (BMI), ASA score, type of surgery, and pathological staging revealed no differences between the groups regarding tumour differentiation, staging, or postoperative complications. Survival analysis at 6 years showed no significant difference in overall survival between the SRC (53.2%, 95% CI: 35%–71%) and PRC (50.3%, 95% CI: 36%–64%) groups (p = 0.61).

Retrospective design and reliance on electronic medical records from a single institution.

Patients with PPC developed SRC up to 10 years after radiation therapy. Patients with SRC were typically older with more comorbidities. Fewer patients with SRC underwent neoadjuvant therapy, and as a group, required more extensive surgeries with a lower rate of sphincter preservation compared to patients with PRC. Despite these differences, patients with SRC had similar pathological outcomes and overall survival compared to patients with PRC.