637 Background: Phenotypic subtypes for CRC are reported to stratify outcomes. The four subtypes are based on features within the consensus molecular subtypes (CMS): immune, canonical, latent and stromal. In 81 pts, we recently reported concordance between CMS and phenotypic subtypes. Of note, the stromal subtype matched the CMS4 subtype in 84%. Local recurrence (LR) after rectal cancer surgery remains a problem. Identifying those at risk determines who should receive neoadjuvant therapy (NT) and guides surgery. We evaluated whether phenotypic subtypes are associated with LR after radical treatment of rectal cancer. Methods: From a CRC database, pts with rectal cancer and phenotypic subtyping available were identified. Subtyping was performed based on immune cell infiltrate, stromal volume and tumor proliferation. LR was considered pelvic or peritoneal. Results: Between 1997-2007, 260 pts had surgery for rectal cancer. Most were > 65yrs (63%), male (58%) and TNM stage II (39%) or III (37%). 32 (13%) received NT. For phenotypic subtypes, 88 (35%) were Immune, 47 (19%) Canonical, 48 (19%) Latent and 67 (27%) Stromal. Median FU was 138 months (min 88). 70 pts (27%) developed recurrence: LR in 23 (8.8%) and systemic in 44 (16.9%). LR was associated with higher T stage (pT1-3 7% vs pT4 17%, p = 0.024), presence of vascular invasion (15% vs 6%, p = 0.018), serosal involvement (21% vs 6%, p = 0.001), margin involvement (22% vs 7%, p = 0.010), > 50% tumor stroma (18% vs 3%, p = 0.002) and phenotypic subtype (immune 5%, canonical 6%, latent 4% and stromal = 21%, p = 0.002). Similar LR rates were obtained after excluding pts who had NT: Immune (4%), canonical (4%), latent (5%) and stromal (23%). Of the 23 LRs, most were Stromal subtype (n = 14) vs Immune (n = 4), Canonical (n = 3) and Latent (n = 2). Apart from increased node positivity (50% vs 30-44% p < 0.05), there were no differences in rates of pT4 disease, tumor grade, vascular invasion, serosal involvement and margin positivity between stromal subtype and other groups. Conclusions: LR after rectal cancer surgery was associated with the stromal subtype. Validation is needed but pre-treatment tumor subtyping may identify subsets at risk of LR and have implications for patient selection for neoadjuvant therapy.
ISR for T1-2 Low Rectal Cancer: A Japanese Approach
