Molecular assessment of depth of myometrial invasion in stage I endometrial cancer: a model based on K-ras mutation analysis

Abstract

Introduction Overall nearly 20% of endometrial cancer (EC) patients die of the disease and over half of these had initially presented with clinical stage I disease. There is a strong correlation between disease mortality and depth of myometrial invasion. Current assessment of depth of invasion relies on light microscopy. Tumor cells can evade detection by light microscopy if they are vastly outnumbered by myometrial cells. Molecular techniques have a great potential in the detection of such isolated cells. Objective The objective was to develop a model for the application of molecular techniques to advance the assessment of risk status in patients with clinical stage I EC. Methods The study sample included 21 stage I ECs with a documented K-ras mutation from two series of 96 and 106 ECs from the United Kingdom and Norway, respectively. K-ras was documented using heteroduplex mobility analysis and amplified created restriction site, followed by sequencing to identify the specific base substitution at codon 12 and 13 of K-ras oncogene. For each case with a K-ras mutation, a modified mutant allele-specific amplification technique was carried out on a series of tissue strips microdissected at increasing depths from the myometrium underlying tumor. The microdissected myometrium had been previously examined histologically for absence of infiltrating tumor cells on light microscopy. Presence of K-ras mutations was used to identify the tumor cells within the histologically normal myometrium. Correlations between submicroscopic myometrial tumor cell infiltration and clinicopathological factors were studied. Results Of 21 cases with K-ras mutation, 6 cases (28%) showed molecular evidence of tumor cell infiltration beyond the histological boundary. The depth of submicroscopic myometrial infiltration was found to be variable. The staging of the tumors would have changed in 3 cases (14%) if tumor cells been detected histologically. A borderline significant correlation between presence of submicroscopic myometrial invasion and depth of myometrial invasion was noted ( P = 0.053). The recurrence rate and survival of patients without submicroscopic invasion were better than those with, although it did not reach statistical significance (recurrence rate P = 0.13, recurrence free survival P = 0.14, cause-specific survival P = 0.12, and total survival P = 0.2). Conclusions Molecular assessment of depth of myometrial invasion using K-ras mutation is feasible and may add information to conventional light microscopy. Further prospective studies are required to define the clinical significance of this technology.