A type of breast cancer that's notoriously difficult to spot in routine mammograms is becoming much more common, according to new research that highlights a concerning trend in women's health.

Rates of invasive lobular carcinoma have increased by nearly 3% each year over the past decade, according to research published by the American Cancer Society. In comparison, rates of all other breast cancers have risen by just under 1% a year.

Invasive lobular carcinoma — or ILC — is now behind more than one in 10 cases of breast cancer nationwide. That's about 47,000 people a year.

ILC begins in milk-producing glands and then spreads to nearby tissue. It's hard to detect because the cancer cells don't form a defined mass that shows up in mammograms.

Instead, it spreads in thin strands that appear as normal breast tissue on medical images.

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Doctors say that because ILC is strongly linked to hormones, changes in hormone exposure could be a contributor. The ages at which women have children and start menopause have shifted over the years.

Rising rates of obesity and alcohol use could also be to blame.

Doctors say a breast ultrasound or breast MRI can provide a more detailed view of this elusive cancer and are especially important to consider if you have a higher risk or family history of breast cancer.

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