There’s more news on cancer screening tests — this time for women.

Scientists advising the government say a Pap test is a good way to screen young and middle-aged women for cervical cancer, and it’s only needed once every three years. However, they say there is not enough evidence yet to back testing for HPV, the virus that causes the disease.

That’s at odds with the American Cancer Society and other groups, which have long said that using both tests can be an option for women over 30.

Those groups and the government advisory task force separately plan to release proposed new guidelines for cervical cancer screening on Wednesday and invite public comment. The task force is the same group that recommended against routine PSA tests to screen for prostate cancer, saying they were doing more harm than good for men at average risk.

Cervical cancer screening is a success story. In the United States, cases and death rates have been cut more than in half since the 1970s because of Pap smears — lab exams of cells scraped from the cervix, the gateway to the uterus. The test can find early signs of this slow-growing cancer and treat them before a tumor has a chance to develop.

So “the bar is set pretty high” for a test to replace or supplement Paps, said Dr. Evelyn Whitlock of Kaiser Permanente Northwest’s Center for Health Research in Portland, Ore.

Not enough is known about the benefits and especially the harms of HPV testing, concludes the scientific review she led that was published on Monday. The task force that asked for the review voted unanimously in March that there was insufficient evidence to recommend for or against HPV testing, but has continued to discuss the issue and will give its advice on Wednesday.

Here’s the dilemma: Infections with HPV, the human papillomavirus, are very common especially in young women. They usually go away on their own and only pose a cancer risk when they last a year or more.

Tests that find these infections might lead many women to more invasive follow-up tests that can weaken the cervix and cause problems having children later. No big studies measure these harms, and a test that flags more potential cancers might not be better.      

“A lot of people use the word ‘superior’ to mean it catches more cancer. But the other side of it is, does it catch more things that are not cancer? You have to weigh benefits versus harms for any screening test,” said Debbie Saslow, the cancer society’s director of breast and gynecologic cancer.

The evidence review finds little risk of cervical cancer in women under 21 and says screening below that age may be harmful. It also says screening can stop at age 65 if a woman has had adequate screening in the past and is not otherwise at high risk.

The review was published Monday in the Annals of Internal Medicine.

The same journal also published a study on another women’s cancer issue — breast cancer screening. That research supports having mammograms every other year instead of annually. Over time, there are more false alarms with annual screening, and going every two years does not significantly raise the risk of a late-stage cancer being found, researchers report.

Breast cancer screening has been an emotional issue since 2009 when the government task force said women at average risk of the disease don’t need mammograms until age 50 and then just every other year to age 74. The cancer society and others still advise annual tests starting at age 40.

The federally funded study gives a real-world view of the downside of screening — the worry, expense and medical risks of biopsies and other tests that ultimately prove unnecessary. It looked at false alarms at various intervals of screening for nearly 170,000 women ages 40 to 59 in ordinary community settings, plus nearly 4,500 other women with invasive breast cancer.

About 61 percent of women who get a mammogram every year for a decade will be called back at least once for extra tests that turn out not to show breast cancer, the study found.

Screening every other year drops this false alarm rate to 42 percent without a big risk of cancer being discovered at a late stage. A tip for women: If you changed where you go for mammograms, bringing or having doctors send your last one to be compared to the new one cuts in half the chance of a false alarm.

Women who started having mammograms in their 40s versus their 50s were more likely to have a false alarm just because they were having more tests — not because mammography is less accurate in that age group.

False alarms “are part of the price to pay for early detection,” said study leader Rebecca Hubbard of Group Health Research Institute, part of a Seattle-based managed care system. Women need to know how common they are, and “if it happens to them they will feel less anxiety,” she said.

Dr. Robert Smith, the cancer society’s director of cancer screening, said the study should have more precisely defined intervals — it called annual screening an interval of 9 to 18 months, and biennial screening, 19 to 30 months.

“A false positive is commonly discussed as if it were a catastrophic event. For the large majority of women, it isn’t,” and surveys say women will accept the risk in return for finding cancer early, he said.

Online:

Journal studies: www.annals.org

Cervical cancer science review: http://tinyurl.com/6lc2rzg

Task force advice: http://www.ahrq.gov/clinic/pocketgd1011/gcp10s2.htm

CDC on HPV tests: http://www.cdc.gov/hpv/Screening.html

Cancer Society: http://tinyurl.com/44gnadx

and http://tinyurl.com/257mnge