Colorectal Cancer

ASCO 2016. Abstract 3504. Impact of primary (1º) tumor location on overall survival (OS) and progression-free survival (PFS) in patients (pts) with metastatic colorectal cancer (mCRC): Analysis of CALGB/SWOG 80405 (Alliance).

Alan P. Venook et al.

Results: KRAS wt pts: Median age = 59; synchronous = 78%. 1° site: R – 280 (25%); L – 689 (61%); T- 62 (5%); unsure – 106 (9%). OS & PFS (Table) difference by side statistically significant if adjusted for age, gender, BV / Cet, chemotherapy, prior therapy. There was a significant 1° side by biologic interaction (P int = 0.003, PFS and OS) but not by chemo, gender or RAS. OS, L-sided: Cet v BV, superiority (Log rank p = 0.04); R-sided: BV v Cet, superiority (p = 0.03). Results similar for PFS and if T colon allocated to R side. KRAS mut pts: 1°s: R – 35%; L- 50%. No statistically significant difference in any subset although OS favors L > R (only OS data shown).

Conclusions: mCRC arising in the R v L colon are clinically different. In KRAS wt mCRC, pts w/ L-sided 1° tumor have superior OS and PFS v pts w/ R-sided 1°. Though not pre-planned analyses, OS and PFS were prolonged w/ Cet in L and w/BV in R but were poorer w/ Cet in R. Forthcoming molecular analysis of 1°s – e.g. BRAF, MSI, methylation – may provide a biological explanation. For now, stratification in mCRC studies by R v L 1° sidedness is indicated. These data support BV in 1st line treatment for mCRC pts w/R-sided 1° tumour regardless of KRAS status. Clinical trial information: NCT00265850

CARE™ Faculty Perspective: This was an interesting study as it investigated whether the primary tumour location in mCRC had an impact on survival. Irrespective of which biologic patients received, patients with metastatic disease who have right-sided primary CRC, do worse than patients with left-sided CRC. This raises questions about the molecular biology of proximal vs distal cancers, and adds to the understanding of the molecular taxonomy of cancers.