Metastatic invasive lobular carcinoma highly heterogeneous

Patients with de novo metastatic invasive lobular carcinoma (mILC) display unique and heterogeneous clinicopathological characteristics, metastasis patterns, and responses to treatment, a recent study has found.

“Our aim was to describe the features and survival of [these patients], and further subdivide them into subcategories for prognostic stratification and treatment planning,” the researchers said.

Accessing the SEER database, researchers identified 1,675 patients with de novo mILC diagnosed from 2010 to 2018. Participants had an average age of 64.8 years and could be subdivided into three according to metastatic involvement of different organs: M1a (bone or lung involvement only), M1b (liver involvement only, or involvement of bone and lung but no other organ), and M1c (involvement of brain, or of the liver and other distant sites).

Of the three subclasses, M1a was the most common, found in 73.3 percent of patients, followed by M1c (17.7 percent) and M1b (9.07 percent).

Kaplan-Meier curves showed significant prognostic differences across the three mILC subcategories. For instance, overall survival was significantly better in the M1a subclass as opposed to both the M1b (hazard ratio [HR], 1.382, 95 percent confidence interval [CI], 1.106–1.727; p=0.004) and M1c (HR, 2.142, 95 percent CI, 1.818–2.523; p<0.001) subclasses.

Breast cancer-specific survival was likewise significantly greater in the M1a vs M1b (HR, 1.404, 95 percent CI, 1.114–1.769; p=0.004) and M1c (HR, 2.110, 95 percent CI, 1.779–2.502; p<0.001) subclasses.

Moreover, the different subclasses showed markedly different responses to treatment. Primary surgery, for example, had a significantly stronger benefit on M1a patients as opposed to M1b and M1c comparators. In contrast, the M1a subgroup benefited the least from chemotherapy alone.