A new study shows that appendix cancer is becoming more common among younger generations, mirroring a pattern that has been occurring with other cancers since the 1990s.

Cancer incidence rates among members of Generation X were two to three times higher than among people born in the 1940s, according to the study, which was published Monday in the Annals of Internal Medicine. Rates among older millennials, born in the 1980s, were more than four times higher.

Even with those increases, appendix cancer still remains extremely rare. Doctors diagnose an estimated 3,000 new cases in the United States each year, compared with more than 150,000 cases of colon and rectal cancers.

The findings come at a time of growing concern about the earlier onset of certain cancers, including colorectal, breast and kidney cancers. The new research describes what’s known as a “birth cohort” effect, or a disease becoming more common among successive generations. Such an effect lends credence to the idea that people born after a certain time have had similar exposures to something that is increasing their cancer risk more so than among people born decades before, said Dr. Andrea Cercek, a medical oncologist at Memorial Sloan Kettering Cancer Center who was not involved in the study.

And the fact that researchers have seen similar generational effects in colorectal and gastric cancers suggests there may be some shared risk factors between those cancers and appendix cancer, said Dr. Andrew T. Chan, a gastroenterologist at Massachusetts General Hospital who researches the epidemiology of colon cancer and also was not involved in the study.

Diet is one such possibility, he said. Our consumption of ultraprocessed foods has increased over time, and these foods — particularly processed meats and sugar-sweetened beverages — have been associated with increased risk for colon cancer.