WASHINGTON — Cancer researchers say there has been a substantial increase in women under the age of 26 who have received a diagnosis of early-stage cervical cancer, a pattern that they say is most likely an effect of the Affordable Care Act.

Starting in 2010, a provision of the health law allowed dependents to stay on their parents’ health insurance until age 26. The number of uninsured young adults fell substantially in the years that followed. The share of 19- to 25-year-olds without health insurance declined to 21 percent in the first quarter of 2014 from 34 percent in 2010 — a decrease of about four million people, federal data show.

Researchers from the American Cancer Society wanted to examine whether the expansion of health insurance among young American women was leading to more early-stage diagnoses. Early diagnosis improves the prospects for survival because treatment is more effective and the chance of remission is higher. It also bolsters women’s chances for preserving their fertility during treatment. And women with health insurance are far more likely to get a screening that can identify cancer early.

Researchers used the National Cancer Data Base, a hospital-based registry of about 70 percent of all cancer cases in the United States. They compared diagnoses for women ages 21 to 25 who had cervical cancer with those for women ages 26 to 34, before and after the health law provision began in 2010. Early-stage diagnoses rose substantially among the younger group — the one covered by the law — and stayed flat among the older group.