Tissue expression of mismatch repair proteins and tumor lymphocytic infiltration: prognostic significance in resected colorectal carcinoma]

Background. In colorectal cancer there is discussion about the possible relation between the mismatch repair protein expression (MMRPE) and tumour lymphocytic infiltration (TLI), as well as the possible prognostic effect of both factors. Methods. A review was made of 243 colorectal cancers, consecutively resected. We made an immunohystochemical study of the MMRPE of MLH1, MSH2 and MSH6. The TLI was evaluated through CD3 staining in the tumoural epithelium. We compared mortality and post-operative tumoural progression amongst the cases with and without MMRPE and with and without TLI. Additionally, we studied mortality and tumoural progression amongst MMRPE (+) cases, according to whether or not they presented TLI. Results. Thirteen point six percent of the tumours expressed MMRPE (+) and 25.5% TLI (+). The follow-up was: 73.8+/-34.6 months. The frequency of TLI (+) turned out to be similar between MMRPE (+) tumours: 27.3% and MMRPE (-): 25.2% (p = 0.80). The MMRPE (+) cases showed less mortality: 12.1% versus 23.3% (p = 0.15) and less tumoural progression: 21.2% versus 29% (p = 0.35). The ITL neoplasias (+) had a lower mortality: 9.7% versus 26% [p = 0.007; OR = 3.27(1.25-9.05)] and tumoural progression: 12.9% versus 33.1% [p = 0.002; OR = 3.35 (1.42-8.15)]. The 9 MMRPE (+) and ILT (+) tumours did not present mortality or tumoural progression, against a mortality: 16.7% and progression: 29.2% of the 24 MMRPE (+) and TLI (-) cases p = 0.19 and p = 0.07 respectively. Conclusions. No relation was found between MMRPE and TLI, with very similar rates of TLI (+) between cases with and without MMRPE. The TLI (+) showed a favourable prognostic effect higher than that of the MMRPE (+). The combination of TLI (+) and MMRPE (+) seems to have an accumulative protective effect, although its limited frequency reduces the significance of the finding.