Positives and Negatives: Understanding a Breast Cancer Diagnosis

If you’re newly diagnosed with breast cancer — or you have a loved one who recently was diagnosed — it can feel overwhelming. Treatment options depend on the stage of the cancer, how quickly it’s growing and an understanding of other individual factors to achieve the best results.

Is your cancer hormone-receptive? Triple-negative? Is it HER2-positive? HER2-negative? Or something in between, a category newly classified as HER2-low?

All of this can be a lot to digest, but the details do make a difference.

Reshma Mahtani, D.O., chief of breast oncology at Baptist Health Miami Cancer Institute

“Personalized medicine is the wave of the future,” explains Reshma Mahtani, D.O., chief of breast oncology at Baptist Health Miami Cancer Institute. “We aim to give the right drug to the right patient. As we better understand the biological drivers and mechanisms of resistance to therapies, we develop more customized treatment plans. With this approach we’ve seen that patients are living longer and enjoying a better quality of life.”

Understanding Hormone Receptors in Breast Cancer

Knowing the hormone receptor status of your cancer helps doctors determine how to treat it and which chemotherapy to pursue, helping them slow down or stop the cancer’s growth.

Hormone receptors are proteins that can be found on the surface or inside of cells, including breast cancer cells. If a breast cancer cell has these receptors, it means the cancer may rely on the hormones estrogen or progesterone to grow.

These hormones are naturally produced by the body, especially in the ovaries. When they bind to their respective receptors on breast cancer cells, they act like growth signals, encouraging the cancer cells to multiply. This type of breast cancer is more likely to respond to hormone-blocking treatments.

Not all breast cancers have hormone receptors, however. Some breast cancers do not depend on estrogen or progesterone for growth and are known as “hormone receptor-negative.” As a result, they don’t respond to treatments that block or lower these hormones. Other treatments like chemotherapy are usually recommended instead.

What About HER2 Status?

While not directly related to estrogen or progesterone, HER2-positive cancer refers to a protein called human epidermal growth factor receptor 2 (HER2) that can also promote cancer cell growth. Some breast cancers are both hormone receptor-positive and HER2-positive, which influences treatment options.

In about 20 percent of breast cancers, the cancer cells make too much HER2, driving tumor growth. These cancers, known as HER2-positive, tend to spread more aggressively than HER2-negative breast cancers. The treatment of HER2-positive metastatic breast cancer is complex and typically involves a combination of targeted therapies, chemotherapy, hormone therapy (if the cancer is also hormone receptor-positive) and supportive care.

Roughly half of all metastatic breast cancers are classified as HER2-low, which have reduced HER2 readings, but enough that they are still targetable with a novel HER2-targeted therapy.

“Trastuzumab deruxtecan (Enhertu) was initially approved for HER2-positive and now, more recently, for HER2-low metastatic breast cancer — and this therapy has dramatically improved outcomes for our patients in both settings,” explains Dr. Mahtani. “We’ve seen a significant impact. Given the large number of patients with HER2-low metastatic breast cancer, to date many patients have received the drug and are enjoying longer durations of time during which their breast cancer is controlled, while also experiencing an overall good quality of life.”

Guiding the Future of Cancer Care

Researchers are continually developing and testing new drugs and combination therapies.

Dr. Mahtani was co-first author of a study on the sequential use of antibody drug conjugates (ADCs) in patients with metastatic breast cancer. ADCs combine an antibody that targets a protein on the cancer cell, along with potent chemotherapy drugs. They are known as Trojan horses because they deliver anti-cancer treatments directly into tumors. Some ADCs have the additional ability to kill off neighboring cancer cells even though they have a lower expression level of the target.

Dr. Mahtani, who has been active in clinical research for more than two decades, is also principal investigator of a multi-institutional breast cancer clinical trial that will build upon this study. The new study is helping develop more-personalized treatment approaches by clarifying the optimal sequencing of ADCs, which will spare toxicities of therapies to patients who are not likely to benefit.

Miami Cancer Institute doctors are making significant contributions to advances in breast cancer treatment. Most exciting, Dr. Mahtani says, are the breast cancer clinical trials available through Baptist Health Cancer Care, giving patients access to potentially better therapies that are not yet widely available anywhere else.

“These have the potential to change how breast cancer is treated going forward,” Dr. Mahtani says. “These include studies with novel targeted treatments that provide a personalized approach to the treatment of breast cancer, both in the early stage and metastatic setting.”

Clinical research is helping advance science and improve outcomes, Dr. Mahtani says.

“It’s an exciting time in cancer care,” she says. “As a breast medical oncologist, I see so much hope on the horizon as novel therapies and improvements in screening continue to contribute to improved outcomes for patients.”