Paps detect mild abnormalities, called "mild dysplasia," as well as severe lesions that are poised to become cancerous. Regardless of the degree of dysplasia, women often are referred for more in-depth testing called colposcopy, or even a biopsy.
But some doctors have questioned how necessary the extra and expensive care is for women whose dysplasia is mild.
The study, published in this week's Journal of the National Cancer Institute, found that commonly diagnosed cases of mild dysplasia were highly likely to return to normal rather than develop into cervical cancer, reports CBS News Health Correspondent Dr. Emily Senay.
Researchers concluded the risk of mild dysplasia progressing into more severe abnormalities or cancer was only 1 percent per year.
"This study should put to rest the widespread fear that women with mild dysplasia need immediate referral" for in-depth care, instead of just monitoring with repeat Pap smears, University of Washington epidemiologist Cathy Critchlow concluded in an accompanying editorial.
The University of Toronto researchers also suggested that monitoring the condition with repeated Pap smears might be a reasonable alternative to referral for surgery to remove the cells.
Some 50 million women in the United States get a Pap smear every year, a simple test that can detect precancerous cell changes before they turn into cervical cancer.
The Canadian study examined the records of almost 18,000 women diagnosed with dysplasia between 1970 and 1980, and tracked their health through 1989.
Two years after the initial diagnosis, 29 percent of women with mild dysplasia were the same or had worsened. In contrast, women with moderate or severe dysplasia were 2.5 times to 4.2 times more likely to have progressed to worse dysplasia or cancer, the study found.
During 10 years, over 60 percent of the women with mild dysplasia had their abnormal cells revert to normal, the study said.