DISEASE CHARACTERISTICS: Primary colorectal cancer and participating in one of the following NCCTG protocols: NCCTG-784852: No Treatment Control Versus Levamisole Versus Levamisole Plus 5-Fluorouracil NCCTG-794604: No Treatment Control Versus 5-FU by Portal Vein Infusion NCCTG-794751: Postoperative Radiation Versus Postoperative Radiation Plus Sequential Chemotherapy with Methyl CCNU and 5-FU NCCTG-844652: An Intergroup Study - An Evaluation of Levamisole Alone or Levamisole Plus 5-Fluorouracil as Surgical Adjuvant Treatment for Resectable Adenocarcinoma of the Colon NCCTG-864751: Phase III Protocol for Surgical Adjuvant Therapy of Rectal Carcinoma: A Controlled Evaluation of (A) Protracted-Infusion-5-Fluorouracil (5-FU) as a Radiation Enhancer and (B) 5-FU Plus Methyl-CCNU Chemotherapy NCCTG-874651: M/N - A Controlled Evaluation of Recombinant Interferon-Gamma (IFN-GM) and 5-FU and Folinic Acid With or Without Levamisole as Adjuvant Treatment for Resectable Adenocarcinoma of the Colon NCCTG-894651: A Controlled Phase III Evaluation of 5-Fluorouracil with Levamisole and Leucovorin as Adjuvant Treatment for Resectable Colon Cancer NCCTG-914653: A Phase III Evaluation of High-Dose Levamisole Plus 5-Fluorouracil and Leucovorin as Surgical Adjuvant Therapy for High-Risk Colon Cancer Adequate tissue for review OR Families of patients meeting the above criteria OR Colon cancer patient and population controls not in a high-risk family OR Spouse of a high-risk colon cancer patient