Biological effects of preoperative radiotherapy on metastatic lymph nodes from rectal cancer

The quantitative description of the proliferative activity of cancer cells correlates with the aggressiveness of malignant tumors. The aim of this retrospective study was to determine the biological effect of adjuvant therapy on metastatic lymph nodes from rectal cancer and to compare the results between patients treated with surgery alone and patients treated with preoperative radiotherapy. Expression of the proliferating cell nuclear antigen (PCNA) was examined in metastatic lymph node samples of 12 rectal cancer patients receiving and 14 patients not receiving preoperative radiotherapy. PCNA immunostaining was performed by an avidin-biotin complex immunoperoxidase technique. The results of the mean proliferation index (PI) between the two groups were compared. A semiquantitative PCNA grading system was also estimated. In patients receiving preoperative radiotherapy, the PI was 22.8 per cent, and only one patient had high proliferative grade. On the contrary, the PI in nonirradiated patients was 67.6 per cent, and nine patients showed high proliferative grade. Although not sufficient to reach significance in terms of prognosis, the present study confirms the clinical value of radiation therapy, and it supports the suggestion to treat Dukes' C patients with preoperative radiotherapy to decrease the risk of local recurrence.