Impact of preoperative radiation for rectal cancer on subsequent lymph node evaluation: A population-based analysis

PURPOSE: To determine the impact of preoperative radiotherapy (RT) on the accuracy of lymph node staging (LNS). Preoperative RT is a well-established component of rectal cancer treatment but its impact on LNS is unknown. METHODS AND MATERIALS: The Surveillance, Epidemiology and End Results (SEER) registry, representing 14% of the U.S. population, was used to assess the impact of preoperative RT on LNS. Our study population consisted of adults with rectal cancer between 1998 and 2000 who underwent radical resection. RESULTS: In our 3-year study period, 5647 patients met the selection criteria and 1034 (19.5%) underwent preoperative RT. The preoperative RT group was younger (average age, 61 years) than those who did not undergo preoperative RT (average age, 69 years) and more likely to be male (22% of men vs. 16% of women). On average, fewer nodes were examined in patients who underwent preoperative RT (7 nodes) vs. those who did not (10 nodes); this difference was statistically significant, controlling for potential confounders (p < or = 0.0001). In 16% of the preoperative RT patients (vs. 7.5% without), no nodes were identified (p < or = 0.0001). If one used a minimum of 12 nodes as the standard, only 20% of patients who underwent preoperative RT underwent adequate LNS. CONCLUSION: Lymph node staging in patients who undergo preoperative RT must be interpreted with caution. Studies are needed to evaluate the clinical relevance of node number and pathologic staging after preoperative RT for rectal cancer.