Instabilidade de microssatélites em carcinoma colorretal de pacientes jovens por técnicas de biologia molecular em amostras processadas rotineiramente para diagnóstico anátomo-patológico

Abstract

Introduction: Colorectal cancer (CCR) is the second most common neoplasia in the developing countries, after lung cancer in men and breast cancer in women. Microsatellites are repetitive short sequences of nucleotides in all human being genome, susceptible to enlarged or contract itself during DNA replication. Tumors that present deficiency in DNA repair genes (MMR), these expansions or contractions are not repaired, causing microsatellites instability (MSI), that can be high (MSI-H) or low (MSI-L). Microsatellites are considered phenotype markers for prognostic, therapeutic reply and identification of patients withmutations in MMR. Patients with mutations in MMR are supposed to develop hereditary nonpolyposis colorectal cancer (HNPCC) syndrome. MSI was present in the majority of the CCR patients with HNPCC (5%) and about 15% in sporadic tumors. Therefore, MSI evaluation inCCR shows practical importance and in near future its research may be suggested as a complement for diagnosis and prognostic in these tumors. Objectives: To standardize molecular biology method for the detection of MSI in CCR samples from young patients performed routinely for anatomic-pathologic diagnosis, to characterize MSI as high or low, tocorrelate presence and type of MSI with the anatomic-pathologic characteristics of CCR. Material and methods: A total of 48 patients, 40 years old or less, presenting CCR was studied. Selected cases were gotten from material embedded in paraffin. Most adequate tumorareas and normal mucosa from the same patient were selected through optic microscopy in order to perform molecular tests by polymerase chain reaction (PCR). The extractions were carried out using commercial kit. Electrophoreses were performed in polyacrilamide gel. Microsatellites: BAT25, BAT26, D2S123, D5S346 and D17S250[Mfd15CA ] were tested.Results: Adequate DNA for MSI research was extracted in almost all cases, except for one case in which only one microsatellite amplified (BAT26). Microsatellite BAT26 presented higher amplification frequency (100%) and D2S123 presented lower amplification frequency(83.3%), from the total, 21 cases (43.8%) presented stable microsatellites (MSE), 24 cases (50%) presented MSI, 15 cases (62.5%) with MSI-H and 7 cases (29.2%) MSI-L. The majority of CCR (60.5%) was located in left colon and was predominantly annularconstrictive(39.6%). Lymphocytic reply was discrete or absent in the majority of the cases (58.1%). The majority of the tumors was considered as pT3 (67.4%) and 14 cases (38.9%) showed metastasis in lymphonodes. Tumors with instability were more frequent in men and were located preferentially in right colon and lymphocytic reply was the most frequent found. Conclusions: The result of the detention of DNA allelic amplification varied according to the tested microsatellites. The most sensible microsatellite was BAT26 (100%) and the least sensible was D2S123 (83.3%). The frequency of MSE cases was lower than MSI cases.Among unstable cases, the frequency of MSI-H cases was higher than MSI-L cases. In MSI-L cases the instability in the mononucleotides microsatellites was not found (BAT25 and BAT26). CCR with MSI was more frequent in men and was located preferentially in right colon, with annular-constrictive macroscopy, peritumoral lymphocytic reply from discrete to moderate.