Scientists are sounding the alarm about a rare but highly lethal type of cancer that is increasingly on the rise in the US, with incidences growing three times faster than other cancer forms.

An important observation from 2012 to 2021 revealed that the incidence of invasive lobular carcinoma (ILC), a form of breast cancer, increased at an average annual rate of 2.8 percent in women aged 50 and older, and 2.9 percent among women under 50.

This rise across age groups exceeds the 0.8 percent increase for all other breast cancers combined. 

The years 2016 to 2021 were particularly alarming, showing a more pronounced annual rise of 3.4 percent. Experts indicate that hormonal and lifestyle factors, rather than genetic ones, are the main contributors to the increasing rates of invasive lobular carcinoma.

This week, researchers from the American Cancer Society noted that the sharpest surge in lobular breast cancer cases was observed among Asian American/Pacific Islander (AAPI) women, with an annual increase of 4.4 percent.

Despite this significant rise, white women continue to have the highest overall incidence rate, with nearly 15 cases per 100,000 women, versus 11 per 100,000 among Black women, and around seven per 100,000 among AAPI women.

Angela Giaquinto, the lead researcher and an associate scientist for cancer surveillance research at the American Cancer Society, stated, ‘Although lobular breast cancer constitutes just over 10 percent of all breast cancers, the sheer volume of new diagnoses each year makes it crucial to comprehend this ailment.’

The lobular form of the disease appears to grow in ways that differ from the other breast cancers, with cells proliferating in dispersed patterns as opposed to forming a lump typical of other cancers. 

The growth pattern of ILC doesn’t make it categorically more aggressive in terms of metastasis, but it makes its spread differently, sometimes later, and to unusual locations, which poses unique challenges for detection and treatment.

Researchers analyzed national cancer data, comparing invasive lobular breast cancer cases against all other types to track incidence trends. 

Using specialized software, they calculated rates and tested for statistical differences in trends. 

The study also compared patient and tumor characteristics between lobular and ductal cancers and analyzed their ten-year survival rates. 

While ILC has a similar five-year survival rate to other breast cancers, its long-term outlook is less favorable. 

The ten-year survival rate is lower, largely because ILC has a higher risk of late recurrence and tends to spread to uncommon sites in the body.

For lobular cancer that has spread distantly, the 10-year survival rate is only 12.1 percent compared to 19.6 percent for the more common ductal cancer.

Lobular breast cancer is becoming more common, and its long-term survival rates are low once it spreads.

In addition to finding that rates of ILC are rising over three times faster than all other breast cancers, its slight survival advantage in the first few years disappears over time.

Giaquinto said: ‘Also, survival rates beyond seven years are significantly lower for [lobular breast cancer] than the most common type of breast cancer, highlighting the pressing need for prevention and early detection strategies targeting this subtype to be brought to the forefront.’ 

The authors conclude that ILC’s unique biology, which makes it harder to detect and potentially less responsive to chemotherapy, requires specific research and clinical attention to improve these outcomes.

Senior researcher Rebecca Siegel, senior scientific director for cancer surveillance research at the ACS, said: ‘Invasive lobular breast cancer is very understudied, probably because of a very good short-term prognosis.

‘But at 10 years, these women with metastatic disease are half as likely to be alive as their counterparts with ductal cancer, probably because of the unique spread and resistance to therapy.’

Cases are occurring consistently across all age groups. 

The uniform pattern is notable because ILC is rising at similar rates in both younger and older populations, unlike some other breast cancer types that typically show more variation between age groups.

Researchers pointed to hormonal and lifestyle risk factors as the main drivers of the increasing incidence over genetics. 

ILC is described as being ‘more strongly associated with female hormone exposure’ than other breast cancers, evidenced by a steeper drop in ILC cases when menopausal women’s use of hormone therapy went down.

They also specifically pointed to the impacts of increasing rates of excess body weight, a younger age at first menstruation and having fewer children or having a first birth at an older age.

Factors that extend a woman’s lifetime exposure to estrogen, such as a later age at menopause, along with increased alcohol consumption in some groups, are also identified as significant contributors to the growing number of cases.

Their research was published in Cancer, the journal of the American Cancer Society.  

Siegel concluded: ‘Our study underscores the need for much more information on lobular cancers across the board, from genetic studies to clinical trial data, so we can improve outcomes for the increasing number of women affected with this cancer.’