Let's Talk About Cancer — Part 2: Understanding HER2 and Other Cancer Biomarkers
Kayla Cares | October 15, 2026(I forgot to publish this, i’m so sorry)
Last week, we talked about what cancer is, what can cause it, and why there isn't one single cure.
This week, we're going to talk about something that can sound extremely confusing when you first hear it.
HER2-positive. HER2-negative. Estrogen-positive. Progesterone-positive. Triple-negative.
That's a lot of medical terminology.
And imagine hearing all those words while you're already trying to process being told that you or someone you love has cancer.
You might be wondering:
What does any of that mean? Is one worse than another? Does it change the treatment?
The answer to that last question is yes.
And that's exactly why I wanted to dedicate an entire blog to understanding these differences.
Because two people can have breast cancer and still have very different diagnoses, treatments, and outcomes.
First, What Are Cancer Biomarkers?
Let's start with the word biomarker.
A biomarker is something doctors can measure in the body or in cancer cells that gives them information about a disease.
In breast cancer, doctors commonly test for certain proteins called receptors.
Think of receptors almost like little antennas on a cell.
They receive signals that can tell the cell to grow or perform certain functions.
Some cancer cells use those signals to grow.
By identifying which receptors are present, doctors can better understand how the cancer behaves and which treatments might work.
According to the National Cancer Institute, testing for estrogen receptors, progesterone receptors, and HER2 is an important part of diagnosing breast cancer and planning treatment.
Research: National Cancer Institute — Breast Cancer Biomarker Tests
What Is HER2?
HER2 stands for Human Epidermal Growth Factor Receptor 2.
It's a protein that helps regulate cell growth.
Normal breast cells have HER2 proteins, but some breast cancer cells produce too much of this protein because of changes involving the HER2 gene.
When that happens, the cancer cells can receive stronger signals telling them to grow and divide.
This is called HER2-positive breast cancer.
HER2-Positive Breast Cancer
HER2-positive breast cancers tend to grow and spread faster than many HER2-negative cancers.
That sounds frightening, doesn't it?
But here's something important.
HER2-positive does not automatically mean someone has a worse outcome.
Researchers have developed medications that specifically target HER2.
These treatments have dramatically changed how doctors manage HER2-positive breast cancer.
According to the American Cancer Society, approximately 15–20% of breast cancers are HER2-positive.
That's roughly 1 in every 5 to 7 breast cancers.
Treatments may include HER2-targeted medications such as trastuzumab (Herceptin), sometimes combined with chemotherapy or other treatments.
These medications are designed to interfere with signals that help HER2-positive cancer cells grow.
They don't guarantee a cure, but they have made a major difference in treatment.
Research: American Cancer Society — Breast Cancer HER2 Status
What About HER2-Negative Breast Cancer?
HER2-negative means the cancer does not meet the criteria for being HER2-positive.
But here's where things get interesting.
HER2-negative does not mean the cancer is harmless.
It also doesn't mean there aren't treatments available.
Some HER2-negative cancers respond to hormone therapy, chemotherapy, or other targeted treatments.
And scientists have learned that even within the HER2-negative category, there can be important differences.
HER2-Low and HER2-Ultralow
You may have heard these newer terms.
HER2-low means cancer cells have a small amount of HER2 protein but not enough to be classified as HER2-positive.
HER2-ultralow refers to an even smaller detectable amount.
Why does this matter?
Because newer medications, including certain antibody-drug conjugates, can help some people with advanced breast cancer whose tumors have low or ultralow HER2 expression.
These drugs combine an antibody that recognizes a target on cancer cells with a cancer-fighting medication.
It's another example of how cancer treatment continues to evolve.
Research: American Cancer Society — HER2 Testing and Results
Estrogen and Progesterone Receptors
Now let's talk about hormones.
Our bodies naturally produce hormones, including estrogen and progesterone.
These hormones have important functions, but certain breast cancer cells have receptors that allow hormones to encourage their growth.
Doctors test breast cancer cells to determine whether they have these receptors.
Estrogen Receptor-Positive (ER+)
This means the cancer cells have estrogen receptors.
Estrogen can help these cells grow.
Progesterone Receptor-Positive (PR+)
This means the cancer cells have progesterone receptors.
Progesterone-related signaling can also influence the cancer cells.
Hormone Receptor-Positive (HR+)
If a breast cancer has estrogen receptors, progesterone receptors, or both, it is considered hormone receptor-positive.
According to the American Cancer Society, approximately 3 out of 4 breast cancers have at least one of these hormone receptors.
That's a significant majority.
And it matters because these cancers may respond to hormone therapy.
Despite its name, hormone therapy for breast cancer generally works by reducing hormone production or blocking hormone effects that encourage cancer growth.
Medications such as tamoxifen and aromatase inhibitors may be used, depending on the patient's circumstances.
Research: American Cancer Society — Breast Cancer Hormone Receptor Status
What Is Triple-Negative Breast Cancer?
This is another term that can sound intimidating.
Triple-negative breast cancer means the cancer tests negative for three major biomarkers:
Estrogen receptors (ER)
Progesterone receptors (PR)
HER2 overexpression or amplification
In simpler terms, the cancer doesn't have the usual targets for hormone therapy or standard HER2-targeted treatments.
That can make treatment more challenging.
Triple-negative breast cancer often grows more quickly and has a higher risk of recurrence than some other breast cancer types, particularly during the first several years after diagnosis.
But that does not mean it cannot be treated.
Depending on the stage and other characteristics, treatments may include chemotherapy, immunotherapy, surgery, radiation, or certain targeted medications.
Research continues to improve the options available.
And I think it's important to remember:
A more aggressive cancer does not automatically mean there is no hope.
Research: National Cancer Institute — Breast Cancer Types
What Is Triple-Positive Breast Cancer?
You might also hear the term triple-positive.
This means the cancer is:
Estrogen receptor-positive
Progesterone receptor-positive
HER2-positive
Because the cancer has both hormone receptors and HER2, doctors may be able to use treatments that target both pathways.
For example, someone might receive HER2-targeted medications along with chemotherapy and hormone therapy at different points in their treatment.
Again, this depends on the individual diagnosis.
How Do Doctors Find Out Which Type Someone Has?
Usually, these results come from a biopsy.
During a biopsy, a small sample of suspicious tissue is removed and examined in a laboratory.
A pathologist studies the cells and may perform additional testing.
For HER2, two commonly used tests are:
IHC (Immunohistochemistry): Measures HER2 protein expression in the cancer tissue.
ISH or FISH (In Situ Hybridization): Examines whether the cancer cells have extra copies of the HER2 gene.
HER2 IHC results are commonly reported as 0, 1+, 2+, or 3+.
A result of 3+ generally indicates HER2-positive cancer. A 2+ result usually requires additional testing to determine HER2 status.
The results help the oncology team decide which treatments may be effective.
And here's something that surprised me when learning more about this:
Cancer biomarkers can sometimes change over time.
If cancer returns or spreads, doctors may recommend another biopsy to see whether the cancer's characteristics have changed.
Research: National Cancer Institute — Breast Cancer Diagnosis
Why Two People With Breast Cancer Might Receive Different Treatments
Imagine two women sitting in the same oncology waiting room.
Both have breast cancer.
One is HER2-positive.
The other is hormone receptor-positive and HER2-negative.
Even though they have cancer in the same organ, their treatment plans might look completely different.
One may receive HER2-targeted medications.
The other may receive hormone therapy.
Another person with triple-negative breast cancer may receive chemotherapy combined with immunotherapy.
Their treatment plans also depend on the cancer's stage, grade, genetic characteristics, other medical conditions, and individual circumstances.
This is why comparing one person's cancer journey to another's can be misleading.
There is no one-size-fits-all treatment plan.
And just because one person had a certain treatment doesn't mean that treatment would be right for someone else.
Does HER2 Status Tell You How Advanced Cancer Is?
This is something I especially want to clarify.
HER2 status and cancer stage are not the same thing.
HER2 describes a biological characteristic of the cancer.
Cancer stage describes factors such as the size and extent of the tumor, lymph node involvement, and whether the cancer has spread.
Someone can have early-stage HER2-positive breast cancer.
Someone else can have advanced HER2-negative breast cancer.
The word positive does not automatically mean advanced, and negative does not automatically mean safe.
Both the stage and the biomarkers help doctors understand the diagnosis.
What About Other Biomarkers?
HER2, estrogen receptors, and progesterone receptors are some of the most important breast cancer biomarkers, but they aren't the only ones.
Doctors may also evaluate:
Ki-67: A marker associated with how actively cancer cells are dividing.
BRCA1 and BRCA2: Certain inherited or tumor-related gene changes that may affect cancer risk and treatment decisions.
PD-L1: A biomarker that may help guide immunotherapy decisions in some cases.
PIK3CA: A gene that can have changes relevant to certain targeted treatments.
Multigene tests: Tests such as Oncotype DX that may help estimate recurrence risk and guide chemotherapy decisions in selected patients.
Not everyone needs every test.
The oncology team decides which tests are useful based on the specific cancer and the decisions being made.
Research: American Cancer Society — Breast Cancer Gene Expression Tests
Something I Want Everyone to Remember
When someone tells you they have breast cancer, it's easy to immediately think you understand what they're facing.
Maybe your grandmother had breast cancer.
Maybe your mother did.
Maybe a friend went through chemotherapy.
But their experience doesn't necessarily tell you what another person's journey will look like.
Two people can have the same general diagnosis and still experience different treatments, side effects, challenges, and outcomes.
And I think that's one reason we need to be careful about saying things like:
"Well, my aunt had that, and she was fine."
Or:
"My friend had breast cancer, and her treatment was completely different."
Those statements may come from a good place, but they don't always help.
Instead, maybe we should ask:
"What have your doctors told you?"
"Do you want to talk about it?"
"Is there anything I can do to make things easier?"
Because understanding cancer isn't just about memorizing medical terms.
It's about understanding that every diagnosis belongs to an individual person.
And that person deserves to be heard, respected, and supported.
Coming Next: Understanding Cancer Treatments
Next Thursday, October 22, we'll take a closer look at cancer treatments.
We'll talk about chemotherapy, radiation, surgery, immunotherapy, targeted therapy, and hormone therapy.
We'll also discuss common side effects, why treatment plans can differ so much, and what these treatments actually do inside the body.
Because hearing the word chemotherapy is one thing.
Understanding what it does and why someone may need it is another.
Until then, remember that knowledge can help replace some of the confusion with understanding, even when the situation itself remains frightening.
With love,
Kayla
Kayla Cares LLC
Educational Disclaimer
This blog is intended for general educational and awareness purposes only. I am not a physician, and this information should not replace medical advice, diagnosis, or treatment from a qualified healthcare professional. Cancer diagnoses and treatment plans are highly individualized. Always speak with a qualified oncology team about specific test results, treatment options, and medical concerns.
Research Sources and Further Reading
National Cancer Institute — Breast Cancer Biomarker Tests
Explains HER2, hormone receptors, and other biomarkers used in breast cancer diagnosis.American Cancer Society — Breast Cancer HER2 Status
Explains HER2-positive, HER2-negative, HER2-low, and HER2-ultralow classifications.American Cancer Society — Hormone Receptor Status
Reviews estrogen and progesterone receptors and how they affect treatment.National Cancer Institute — Breast Cancer Types
Describes triple-negative breast cancer and other breast cancer types.National Cancer Institute — Breast Cancer Treatment
Provides detailed, evidence-based information about treatment approaches for different breast cancer subtypes.American Cancer Society — Breast Cancer Gene Expression Tests
Explains how tests such as Oncotype DX may help guide treatment decisions.
