Timing of metastatic dissemination in primary colorectal cancer correlates with tumor aggressiveness

Abstract

3666 Background: Microscopic evaluation of colorectal cancer confirms the presence of tumor, classifies degree of differentiation and defines pathology stage. Morphologic analysis does not define tumor biological aggressiveness or treatment responsiveness on an individual patient basis. We developed and evaluated here a tissue microdissection approach targeting multiple microscopic sites with detailed molecular characterization of colorectal cancer that delineates the unique timeline of mutation accumulation and timing of metastatic dissemination for each cancer. Methods: 21 colorectal cancer patients with T1N1 (n=4), T2N1/M1 (n=7), T3N1/M1 with poor outcome (n=5) and T3N1 long survival (n=5) disease were microdissected using unstained formalin fixed, paraffin embedded standard tissue sections. Microdissection targets consisted of one non-neoplastic site, two sites of greatest primary site invasion and multiple lymph node and hepatic metastasis. Each microdissected sample was quantitatively genotyped and time course determined using a broad panel of mutational damage including k-ras-2 point mutation and LOH for 1p,3p,5q, 9p,10q,17p,17q,21q,22q. Results: There was a progressive increase in acquired discordant mutational change between primary and metastatic sites (T1[0–2]<T2[2–4]<T3[4–8] correlating with metastasis from precursor cells at an earlier stage of invasion. Total mutational load was higher in T3N1/M1 patients with poor survival than for those with good survival (p<.001). For T3NI neoplasms, metastatic precursor cell at the time was deeper (more recent) in the bowel wall than for patients with poor overall survival (p<.01). Liver metastasis could be shown to have arisen from precursor cells in the primary site and not from lymph node metastasis. Conclusions: Aggressive colorectal cancer possesses a high cumulative mutational load with timing of metastasis occurring early in bowel wall invasion. Indolent colorectal cancer of equal T stage shows a lower level of mutations with later timing of metastasis. Microdissection based mutational profiling can characterize colorectal cancer biological aggressiveness in a new and biologically meaningful manner. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration RedPath Integrated Pathology RedPath Integrated Pathology RedPath Integrated Pathology RedPath Integrated Pathology