Invasive lobular carcinoma, the second most common type of breast cancer, accounted for 11% of invasive breast cancers in the United States between 2017 and 2021, according to recent registry data.
Researchers found that Invasive lobular carcinoma (ILC) incidence increased by nearly 3% annually from 2012 to 2021 across all racial and ethnic groups. By 2021, the rates reached approximately 14 cases per 100,000 women, with White patients having the highest incidence (15 per 100,000). Investigators projected about 33,600 ILC cases by 2025.
ILC was most often diagnosed in older patients, with a median age of 66 years compared with 63 years for invasive ductal carcinoma (IDC). More than half of ILC cases occurred in patients aged 65 years and older. Most tumors were hormone receptor (HR)–positive and human epidermal growth factor receptor 2 (HER2)–negative (90%), and 5% were HER2-positive. Tumors tended to be larger at diagnosis, with 14% measuring at least 5 cm vs 7% of IDC tumors.
At diagnosis, 66% of ILC cases were localized, 27% were regional, and 6% were distant. Seven-year relative survival was similar for ILC and IDC (90% vs 90%), but 10-year survival was lower for regional disease (76% vs 78%) and distant disease (12% vs 20%). Findings were consistent when restricted to HR-positive cases.
Data were derived from the National Program of Cancer Registries and the Surveillance, Epidemiology, and End Results Program, covering more than 90% of the US population. Incidence rates were age-adjusted to the 2000 US standard population and corrected for reporting delays. Trends were assessed using Joinpoint regression to calculate the average annual percent change. Ten-year relative survival was assessed for cases diagnosed between 2007 and 2021, with follow-up through 2022.
Projections for 2025 were based on age-specific ILC proportions applied to overall breast cancer incidence estimates.
The study's limitations included a lack of registry data on patient comorbidities, screening behavior, and risk factors that may influence incidence or survival. Mortality could not be assessed by histology due to death certificates not specifying tumor subtype. The analysis did not distinguish between lobular variants or include recurrence data. Survival estimates were not adjusted for tumor grade, treatment, or access to care, and only first primary cancers were included.
“ILC has unique characteristics that can contribute to delayed detection, resistance to therapy, and poorer prognosis for advanced disease,” Rachel A. Giaquinto, MPH, of the Surveillance Research Program at the American Cancer Society and colleagues, explained. "Distinguishing this breast cancer subtype from ductal carcinoma in research and clinical trials is increasingly important to help identify risk factors, facilitate treatment efficacy, and lead to better understanding of mechanisms of metastasis, all of which will improve outcomes for the increasing number of women diagnosed with this cancer subtype."
Some researchers reported funding outside the submitted work. Others declared no conflicts of interest.
Source: Cancer
