Researchers say the size of breast tumors at diagnosis has decreased since routine screening came along, but they’re getting bigger.

Breast tumors are significantly smaller at diagnosis today than they were in the early 1980s, thanks in large part to better screening.

However, experts have changed screening guidelines in recent years to recommend younger women wait to start annual mammograms in the hopes of reducing overtreatment for an irregular result or false positive on a mammogram.

These changes have been controversial. Some experts are worried that new guidelines could mean missing cancer tumors.

Now, new research has found that doctors are seeing a small increase in tumor size in certain patients since 2000. But some experts are divided about what the study results could mean for patients and screening recommendations.

Since 1983, average tumor size decreased between 10.3 and 27 percent across different age groups.

The most striking change occurred between 1983 and 1993. That’s when routine breast cancer screening came of age.

According to the new research, the average size of breast tumors at diagnosis has been increasing slightly since 2001.

The findings were presented at the 11th European Breast Cancer Conference in Barcelona, Spain. The paper hasn’t yet been published in a peer-reviewed journal.

For the study, the researchers looked at 386,454 women in the United States who received a breast cancer diagnosis between 1983 and 2014. The women were grouped according to age.

There was an overall dramatic decline in breast cancer tumor size since 1983. But the researchers found an unexpected rise in tumor size of 3 percent for 75- to 79-year-olds and 13.3 percent for 50- to 54-year-olds between 2001 and 2014.

The largest tumors have consistently been found in women over age 85.

The researchers say that women with smaller tumors at diagnosis generally have a better outlook. But they don’t have evidence that this increase in tumor size will result in more deaths from breast cancer.

Study co-author Dr. Manon Jenkins of Weston General Hospital in Bristol, England, noted that both routine screening and improvements in treatment have contributed to better breast cancer survival rates. It’s unclear which has played a bigger role.

Dr. Dennis Citrin, medical oncologist at Cancer Treatment Centers of America in Chicago, spoke to Healthline about the abstract.

Citrin points out that women age 80 and above aren’t routinely screened.

He suggests that the study would’ve been more meaningful if it compared the size of screened detected cancers versus those that are clinically detected — meaning those detected by identifying a lump or other sign.

Citrin hasn’t seen an increase in tumor size in his practice, which focuses exclusively on breast cancer.

He says the minor increase in the older age group makes very little difference in treatment.

The real takeaway from the abstract, according to Citrin, is that breast tumors are smaller overall.

“The most important fact is that deaths caused by breast cancer are significantly less likely to occur in women who have regular screening mammograms compared with women who don’t,” said Citrin.

Dr. Michele Carpenter is a breast cancer specialist at St. Joseph Hospital in Orange, California.

“We’re telling an aging population not to screen. And the U.S. Preventive Services Task Force [USPSTF] now recommends mammograms every other year for women 50 and older,” she told Healthline.

“So, yes, we will see bigger tumors if we screen less often. Those of us who see patients on a daily basis feel that a portion of patients who are screened every other year end up with a higher-grade tumor,” she said.

Carpenter says that tumors found between mammograms tend to be more virulent.

“We’re treating things so differently than we did 20 years ago,” she said.

“Instead of only tumor size, we look at prognostic factors of the tumor and treat on an individual basis, which is the most important thing,” she explained.

Carpenter said it will be many years before we know if this increase in tumor size translates into a reduction in survival.

The USPSTF says that the women most likely to benefit from a mammography screening every other year are those between the ages of 50 and 74 who are at an average risk for breast cancer. Women between the ages of 60 and 69 are most likely to avoid breast cancer death due to mammography screening.

Citrin said you could argue whether screening should be done annually or every two years. But women age 50 and above should have breast cancer screening on a regular basis.

“If you look at the most recent meta-analyses looking at all of the published data, it’s quite clear that women who have regular screening mammograms have a lower risk of dying of breast cancer. And that’s the whole goal. It’s not 100 percent effective, and no one would ever claim that. But most studies claim a 15 to 20 percent reduction in mortality with screening,” said Citrin.

While guidelines say most women should start screening at age 50, Citrin says that doesn’t mean younger women shouldn’t consider it.

“Broad guidelines are only that. There are women who have increased risk of breast cancer where regular screening guidelines may not apply. If a 38-year-old’s mother had breast cancer at 42, to tell her to wait until she’s 50 for her first mammogram is absurd,” he explained.

Citrin points out that 25,000 women in the United States between age 40 and 50 receive breast cancer diagnoses annually.

“That’s why I personally prefer earlier screening than waiting until age 50,” he said. “The incidence is lower, so whether you start at 40 or 50 is up for debate. Whether women should have screening mammograms is not. They’re clearly beneficial.”

Citrin says that for the general population, stopping at 75 makes sense.

In his practice, Citrin treats women who have already had cancer in one breast. Because they’re at a slightly increased risk of a second cancer, some of his older patients still get screening mammograms.

“We’re interested in smart screening and not blanket statements. Women should have a screening program based on their own risk,” said Citrin.

Carpenter is concerned that many women are no longer getting clinical breast exams. And the USPSTF and other groups no longer emphasize patient self-exams.

“We expect patients to feel things when doctors don’t check. And without recommending breast self-exams, we’re cutting off our nose to spite our face. Our hope is that women should get to know their bodies well enough to know what’s normal and what’s abnormal,” said Carpenter.

Too many women, Citrin says, wait after finding a lump. They hope they’re wrong or that it will disappear.

This isn’t wise, he cautions.

“If it’s cancer, it should be diagnosed and treated at the earliest possible moment. If it’s not cancer, then why worry unnecessarily? Don’t be dissuaded,” said Citrin.

“Make sure the diagnosis is taken through to completion. No doctor, no matter how experienced, can tell from feeling alone if it’s cancer.”

Citrin says if you’re concerned, don’t stop at a physical exam.

“There are limitations to a physical exam,” he said. “You need an imaging test to find out if it’s a simple or complex cyst or a solid tumor, which would need to be biopsied.”

While mammograms involve a small dose of radiation, he said the risk-benefit ratio is in favor of screening.

He stresses that diagnosing breast cancer early offers a better outlook.

“Treatment is much simpler in terms of smaller cancer. You’re more likely to have breast conserving surgery [lumpectomy] or avoid chemo, although that depends on the biology of the cancer as much as stage,” he said.

He strongly urges women to know their family medical history.

“I’d like to encourage women — at the first inkling they feel anything abnormal — to seek immediate medical attention,” Citrin said.