To estimate the"age" of cancers at the time of diagnosis, we reviewed data on the "time to local/regional recurrence" (LRF) following initial surgical resection for three common cancers, then applied a modified version of Collins' law. We conducted a systematic review of English medical literature to identify studies reporting LRF rates, over time, following surgery alone for breast, lung, or colorectal cancer. Patients who received radiation/hormones/chemotherapy were excluded since these therapies may alter tumor growth kinetics after surgery. For each disease, data were considered in three ways: 1) absolute cumulative LRF rate over time; 2) percentage of LRFs manifest over time (to facilitate comparisons between studies with different absolute magnitudes of LRFs); and 3) weighted average of the percentage of LRFs manifest over time. For breast cancer (based on data from 3043 patients from 5 studies), we found that the median time to LRF was 2.7 years. For lung cancer (based on data from 1190 patients from 4 studies), the median time to LRF was 1.5 years. For rectal cancer (based on data from 3334 patients from 10 studies), the median time to LRF was 1.5 years. Based on Collins' law, the distribution of time to LRF suggests that the age of most of the solid tumors studied was 3 to 6 years.