Factors affecting the number of lymph nodes retrieved in colorectal cancer specimens

Background: Staging of colorectal cancer is dependent on the number of lymph nodes in a surgical specimen that are positive for metastatic cancer. It is generally recommended that a minimum of 12 lymph nodes be examined to ensure adequate staging. It is unclear which factors specifically contribute to variation in the number of lymph nodes retrieved from surgical specimens. This study aims to understand the factors affecting the number of lymph nodes identified in surgical colorectal cancer specimens. Methods: A total of 264 retrospectively collected cases of colorectal cancer surgically treated at the University Health Network in Toronto from 2004 to 2006 were analyzed. We used univariate analyses of variance (ANOVA), and univariate and multivariable linear and logistic regression analyses to study variation in the lymph node number associated with a variety of explanatory variables. Results: The average number of lymph nodes retrieved per case was 18.1, with 70 (26.5%) cases containing fewer than 12. Variation in the lymph node number was greatest between different pathology assistants (p = < 0.001). The mean number of nodes retrieved by different pathology assistants ranged from 12.6 to 29.7. On average, surgery for recurrent cancer removed 6.0 (95% CI 1.2 to 10.9, p = 0.02) fewer lymph nodes than for primary cancer. Each additional year of patient age was associated with retrieval of 0.1 (95% CI 0.04 to 0.2, p = 0.005) fewer nodes, and rectal cancer specimens had 2.7 (95% CI 0.04 to 5.4, p = 0.05) fewer lymph nodes than colon cancer specimens. Conclusion: Most of the variation in the number of lymph nodes identified in surgical specimens from colorectal cancer operations was accounted for by differences between pathology assistants.