LBCA SAB Member, Dr. Rinath Jeselsohn gave a Keynote Lecture at the ESMO Breast Cancer annual congress in Berlin, Germany on May 5, 2026, “Lobular breast cancer: Special treatment considerations (+ novel)”. Dr. Jeselsohn explained that a greater understanding of the biology of invasive lobular carcinoma (ILC) has led to a surge in preclinical studies and retrospective clinical analyses over the past decade that has provided valuable insights into potential therapeutic targets. She explained that findings from both lab and animal studies and from clinical trials and studies conducted by collaborations among the ILC research community has created a deeper understanding of ILC. New findings continue to reinforce that ILC is biologically different from other types of estrogen receptor-positive (ER+) breast cancer, including the more common invasive ductal carcinoma (IDC).
ILC accounts for about 10–15% of all breast cancer diagnoses and is most often hormone (i.e., estrogen and progesterone) receptor-positive (ER+/PR+) and human epidermal growth factor receptor 2-negative (HER2-).
One of the defining features of ILC is the loss of a protein called E-cadherin, usually caused by mutations in the CDH1 gene. Without E-cadherin, lobular cancer cells grow in a unique “single-file” pattern instead of distinct lumps or masses, which makes ILC more difficult to detect on mammograms and other imaging tests. This contributes to the fact that patients with ILC present at diagnosis when tumors are at a later stage and are typically larger when compared to patients with other breast cancer types. And while ILC tends to have a lower rate of recurrence within 5 years of diagnosis, it has a higher risk of recurrence after 5 years than other breast cancer types.
Dr. Jeselsohn shared that researchers are also learning that the estrogen receptors (hormone proteins) in ILC may behave differently from when in other breast cancer tumors and that this can affect the efficacy of the hormone therapy the patient is given. Some studies suggest that aromatase inhibitors such as letrozole and exemestane may provide greater benefit for some patients with ILC than tamoxifen, and others provide information about why ILC may resist hormone treatments when IDC still responds. Additional new studies suggest that there are other proteins that behave differently in ILC than in IDC, such as FOXA1 which may prove to be a good target to try to inhibit with drugs to effectively treat ILC.
Overall, the keynote highlighted how rapidly the field of lobular breast cancer research is evolving. Increasing recognition that ILC is a distinct disease is helping drive more dedicated research, more lobular-specific clinical trials, and the potential for more personalized treatment strategies in the future. The growing number of ILC-focused clinical trials represents progress for the field.
Read more from Dr. Jeselsohn here.