Does breast cancer type and hormone status influence the efficacy of hormone therapy in breast cancer patients?

This study evaluated the efficacy of hormone therapy in patients with two types of breast cancer, invasive ductal breast carcinomas (IDC) and invasive lobular breast carcinomas (ILC) based on hormonal status. 

Breasts are made up of lobules (milk-producing glands) and ducts (tubes that carry the milk to the nipple) surrounded by glandular and fatty tissue. IDC is cancer that begins in the milk ducts but spreads (invades) into the surrounding breast tissue. ILC is cancer that begins in the lobules of the breast and invades the surrounding breast tissue. Some types of breast cancer need estrogen (female sex hormone) to grow. These cancer cells respond to estrogen via its receptor (a protein found on the surface of the cancer cells). They are called estrogen receptor-positve (ER+ breast cancers). Breast cancers that do not need estrogen to grow are called estrogen receptor-negative (ER-). Hormone therapy is usually given to ER+ breast cancer patients to stop the cancer from growing. Tamoxifen (Nolvadex) prevents estrogen from binding its receptor on cancer cells and stops them from growing. Exemestane (Aromasin) decreases the amount of estrogen the body produces, therefore slowing or stopping the cancers growth.  

This phase 3 clinical trial included overall 2603 patients with either IDC (82%) or with ILC (18%). Patients were divided into two treatment groups. Patients in group one were treated with exemestane daily for 5 years and patients in the second group were treated with tamoxifen for 3 years followed by exemestane for 2 years. For all patients a pathologist determined the hormonal status (if the cancer is ER+ or ER-).

After 5 years of treatment, relapse free survival or RFS (defined as the percentage of patients surviving without the cancer returning after a time from treatment) was 86% for patients with IDC and 83% for those with ILC. Efficacy for both hormone treatments was similar in patients with ILC and IDC. However, patients with ER+ breast cancer treated with exemestane alone had showed a 30% improved RFS compared with patients who received tamoxifen and exemestane. In contrast, patients with ER- breast cancer had better outcomes with tamoxifen and exemestane therapy. 

In summary, this research showed that hormone therapy had similar efficacy for both IDC and ILC patients. However, the hormonal status of the cancer influenced the outcomes of these patients.