Aspirin is often praised for its anticancer effects. Numerous studies have suggested that regular aspirin use may help lower the risk of colon polyps and colorectal cancer. Now, a study published in this week's issue of the Journal of the American Medical Association is among the first to link aspirin use and colon cancer survival.
For the study, researchers from Massachusetts General Hospital, Dana-Farber Cancer Institute, and Brigham and Women's Hospital looked at the link between aspirin use and survival among 1,279 adults with stage I, II, or III nonmetastatic colorectal cancer, or cancer that had not spread to distant areas.
The patients had enrolled in two large studies in the 1980s prior to their cancer diagnosis and agreed to answer questions about their health over the years. Researchers followed them through June 2008.
In general, study participants who reported aspirin use after being diagnosed with colorectal cancer had a 29% lower risk of colorectal cancer death and a 21% lower risk of overall death, compared to non-aspirin users. The researchers note that the main reasons reported for aspirin use included headache, arthritis, musculoskeletal pain, and treatment and prevention of cardiovascular disease.
Taking aspirin for the first time after a diagnosis improved a patient's odds even more. Among the specific study findings:
- Patients with colorectal cancer who started regular aspirin use for the first time after diagnosis had a 47% lower risk of colorectal cancer death and 32% lower risk of overall death than nonusers of aspirin.
- The survival advantage was seen only in those with Cox-2-positive tumors. Most colorectal tumors are Cox-2-positive.
Aspirin-Resistant Colon Cancer
The study showed that starting regular aspirin use for the first time after a colorectal cancer diagnosis greatly reduced the risk of colorectal cancer-related death, but taking aspirin before colorectal cancer developed and continuing to do so after diagnosis did not significantly influence survival rates. In other words, former regular aspirin users do not reap as much benefit as those who are new to regular aspirin use.
That might raise an eyebrow or two, particularly since aspirin use has been linked to reduced risk of colorectal cancer.
The researchers say the finding suggests that some colorectal cancer tumors may be resistant to aspirin's effects, while others may be especially susceptible. Aspirin is believed to block a substance called cyclooxygenase-2 (Cox-2). Cox-2 promotes inflammation and cell growth. If the substance is overexpressed, the tumor is called Cox-2-positive; tumors that do not overexpress the substance are called Cox-2-negative tumors.
Cox-2-positive colorectal tumors may be especially sensitive to aspirin's anticancer effects. In the study, the survival improvements were seen primarily among those with such tumors. Specifically, patients with Cox-2-positive colorectal tumors who used aspirin regularly after diagnosis had a 61% lower risk of colorectal cancer death and 38% lower overall death risk than non-aspirin users.
Survival in those with the Cox-2-negative tumors did not appear to be affected by aspirin use.
The new findings could one day lead to aspirin-based therapies for patients with newly diagnosed, early-stage colorectal cancer. However, the researchers do not recommend the routine use of aspirin or related medicines for cancer treatment until further studies are done. Aspirin and other Cox-2 inhibitors can cause potentially dangerous side effects such as gastrointestinal bleeding.
In an accompanying editorial published in the same journal, Alfred I. Neugut, MD, PhD, of Columbia University, adds that aspirin-related survival studies should also be done in patients with metastatic colorectal cancer.