**[675] Multivariate Negative Binomial Regression Identifies Length of Colorectal Resection, Proximal Tumor Location, T3N0M0 Stage, Academic Setting, and Tumor ***PIK3CA* Mutation as Independent Predictors of Lymph Node Count.

*Shuji Ogino, Noriko Tanaka, Charles Fuchs. Brigham and Women's Hospital, Boston, MA; Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA*

**Background:** Lymph node examination in a colorectal cancer resection specimen is important for accurate staging. The number of recovered nodes is associated with improved prognosis. However, little is known on how the lymph node count is influenced by demographic, clinical, pathologic and molecular variables.

**Design:** Utilizing a database of 1124 colorectal cancer patients, multivariate negative binomial regression was used to identify factors associated with the total and negative node counts.

Variables used were sex, age, body mass index, family history of colorectal cancer, hospital setting, year of diagnosis, tumor location, resected colorectal length, TNM stage, tumor grade, mucin, signet ring cells, lymphoid reactions, MSI, CpG island methylator phenotype (CIMP), LINE-1 hypomethylation, *BRAF*, *KRAS *and *PIK3CA* mutations.

**Results:** Because node counts showed gamma-poisson distribution, we used negative binomial regression analysis.

Independent predictors of the negative node count included resected colorectal length (1.27 times more by 20-cm increment, p<0.0001), proximal tumor location (1.36 times, p<0.0001), T3N0M0 stage (1.22-1.72 times, vs. other stages, p<0.0001), and academic hospital setting (1.23 times, p=0.0071) and *PIK3CA* mutation (1.22 times, p=0.0080). Independent predictors of the total node count were similar. The multivariate logistic regression analysis utilizing the total node count as a binary outcome variable (>=12 vs. <12) showed similar predictors.

**Conclusions:** *PIK3CA* mutation and the length of resected colorectum are new independent predictors of the recovered node count. Length of colorectal resection should be examined in future studies to evaluate adequacy of lymph node examination for colorectal cancer.

Category: Gastrointestinal

**Wednesday, March 2, 2011 9:30 AM**

**Poster Session V # 34, Wednesday Morning**