RESUMEN
OBJECTIVE: The objective was to determine the presence and frequency of micrometastasis in lymph nodes of patients with rectal cancer treated by preoperative chemoradiation followed by curative resection. PATIENTS AND METHODS: All 56 patients included were treated with 5-FU and leucovorin plus 5,040 cGy, followed by radical surgery and were diagnosed with stage II distal rectal adenocarcinoma after complete pathological examination (ypT3-4N0M0). Immunohistochemistry was assessed with cytokeratin monoclonal antibody AE1/AE3. Three 4-microm paraffin sections were obtained from each lymph node, cut at 50 microm apart from each other. The results were reviewed by two independent pathologists. RESULTS: Mean number of lymph nodes was 9.6 per patient. Four patients (7%) and seven lymph nodes (1.35%) were positive for micrometastasis. Three patients had pT3 and one a pT4 tumor. One of the patients had positive micrometastasis and the presence of mucinous deposits. One other patient had mucinous deposits without any micrometastasis. All four patients are alive with no evidence of recurrent disease. Fourteen patients negative for micrometastasis had recurrent disease (25%), eight systemic (14.7%) and six locoregional (10.3%). There were two cancer-related deaths. The mean follow-up period was 39 months. CONCLUSION: Patients with rectal cancer treated by preoperative chemoradiation showed a surprisingly low rate of micrometastasis detection (7%), even in high-risk patients (T3 and T4 tumors). Lymph node micrometastasis was not associated with decreased overall or disease-free survival. The identification of mucinous deposits on lymph nodes with no viable tumor cells may be direct evidence of lymph node downstaging. The downstaging effect of preoperative chemoradiation therapy may be significant in reducing even micrometastasis detection in low rectal cancer managed by this treatment strategy.