EXAMINING OPTIMAL SURVEILLANCE STRATEGIES FOR PATIENTS TREATED WITH CURATIVE RESECTION FOR STAGE II OR III COLORECTAL CANCER

Purpose:

To project the long-term effectiveness of intensive imaging-surveillance after curative resection of colorectal cancer (CRC). Intensive imaging surveillance consists of annual abdominal (abdominal-pelvic for rectal cancer) and thoracic CT exam for five years post initial curative resection.

Method(s):

 We developed a state-transition model that simulated newly diagnosed patients with CRC through a series of disease states characterized by (1) a disease free state, (2) the presence of occult micro-metastasis (undetectable by CT), (3) resectable preclinical macro-metastasis (asymptomatic mets potentially detectable by CT and if found is treatable), (4) unresectable pre-clinical macro-metastasis (asymptomatic mets potentially detectable by CT and if found not amenable to curative treatment), (5) symptomatic and resectable disease, (6) symptomatic and unresectable disease, and (7) death (from cancer and other causes). The microsimulation model utilized nonparametric hazard functions to flexibly model the key underlying time to event processes. These were calibrated simultaneously to Surveillance, Epidemiology, and End Results Program (SEER) stage-specific relative survival and the efficacy of imaging-based surveillance taken from a meta-analysis of multiple randomized clinical trials (RCTs). SEER provides relative survival information, which reflects the underlying cancer mortality rates over time. There have been 11 RCTs of intensive surveillance following CRC diagnosis, 8 of which included intensive imaging follow-up (CT, ultrasound, or chest x-ray). The purpose of conducting the CT is to diagnose metastatic recurrence before it becomes symptomatic when it has a greater chance of being resectable (and thereby reducing cancer mortality). 

Result(s):

 Calibrated parameter values showed that the median time to detectable mets was 7 months and the median time to symptomatic disease was 13 months, among those patients destined to develop mets. The model calibrated reasonably well to SEER 5-year relative survival for stage III. A strategy of performing annual CT for five years after CRC diagnosis and curative resection resulted in life expectancy gains of about 9 months for stage III rectal cancer and 12 months for stage III colon cancer. For stage II disease, the absolute improvement in LE was reduced by a factor of about 2, with a LE gain of 4 months for rectal cancer and 5 months for colon cancer.

Conclusion(s):

  Intensive imaging follow-up after curative resection for stage II-III colorectal cancer can effectively reduce cancer-related mortality and thereby increase life-expectancy.