The letters on your report, decoded

Breast cancer treatment is becoming increasingly personalized, but that progress comes with an entirely new vocabulary. PIK3CA. AKT1. PTEN. mTOR. These terms may appear on a biomarker report, or come up when an oncologist is discussing why a treatment stopped working — or what treatment might come next. Together, they are part of the PI3K/AKT/mTOR pathway, often shortened to the PAM pathway. Understanding this pathway will not tell you exactly how your cancer will behave, but it may help explain what is driving it, why biomarker testing matters, and whether a targeted treatment could be an option.

For some people with breast cancer, changes within the PAM pathway can help cancer cells grow, survive, or become less responsive to treatment. Finding those changes through biomarker testing may help your care team identify a treatment designed to target what is driving the cancer.

Understanding the basics can help you ask informed questions, make sense of your test results, and feel more empowered to advocate for yourself when navigating decisions about your care.

The basics

What is the PAM pathway?

The PAM pathway is one of the communication systems cells use to control growth, division, energy use, and survival.

In a healthy cell, the pathway switches on when it is needed and quiets down when the job is complete. In some breast cancers, however, a mutation or another molecular change disrupts this process. The pathway may continue sending growth and survival signals even when it should stop.

When PIK3CA or AKT becomes overly active, or when PTEN no longer functions properly, the cancer cell may gain another way to grow and survive.

Why it matters

Why does this pathway matter in breast cancer?

Changes in the PAM pathway are found across different breast cancer subtypes, but they have become especially important in the treatment of hormone receptor-positive, HER2-negative advanced or metastatic breast cancer.

One of the most commonly discussed changes is a mutation in PIK3CA. This can cause the PI3K protein to remain overly active, sending ongoing signals that encourage the cancer cell to grow.

Alterations involving AKT1 or a loss of normal PTEN function can have a similar effect — by activating other parts of the pathway, or removing the signals that would normally slow it down.

The PAM pathway may also play a role in treatment resistance. A hormone receptor-positive breast cancer may initially rely heavily on estrogen to grow and respond well to endocrine therapy (also called hormonal therapy). Over time, some cancer cells may begin using another signaling system, such as the PAM pathway, to continue growing despite treatment.

Cancer cells can change over time and develop new ways to survive. That is one reason biomarker testing may need to be revisited when cancer returns or progresses.

Testing

What is biomarker testing, and why is it important?

Biomarker testing is different from testing for inherited cancer risk. A hereditary genetic test usually looks for changes you were born with — such as certain mutations in BRCA1, BRCA2, or PALB2, among many others — that may be present throughout the body and passed through families.

Tumor biomarker testing looks primarily for changes that developed inside the cancer cells. These are called somatic alterations. Most PIK3CA mutations found in breast cancer are somatic — meaning they developed in the tumor and were not necessarily inherited from a parent or passed on to a child.

Some people benefit from both hereditary genetic testing and tumor biomarker testing, because the tests answer different questions.

How is the PAM pathway tested?

Testing may be performed using tissue from the tumor, a blood sample, or both. A laboratory may test tissue collected during a biopsy or surgery — and in some cases, previously collected tissue can be used, although a newer sample may provide a more current picture of the cancer.

A liquid biopsy uses a blood sample to look for small pieces of tumor DNA circulating in the bloodstream, known as circulating tumor DNA (ctDNA). Liquid biopsies are less invasive than tissue biopsies and may detect information released by cancer in different parts of the body. However, not every cancer releases enough DNA into the blood to be detected. A negative liquid biopsy does not always mean an alteration is absent.

Treatment

What could a PAM pathway alteration mean for treatment?

Finding a PAM pathway alteration does not automatically determine your next treatment. It does, however, provide another piece of information your oncology team can use when comparing options.

Several medications target different parts of the pathway. Their FDA-approved uses currently focus primarily on specific groups of people with HR-positive, HER2-negative locally advanced or metastatic breast cancer. These medications are not interchangeable — eligibility depends on the exact alteration, previous treatments, timing of recurrence or progression, overall health, and other individual factors.

Does having a mutation mean the treatment will work?

No biomarker can guarantee that a medication will work. A biomarker may tell your care team that a treatment is more likely to help a particular group of patients — but every cancer is complex. A tumor may have several alterations and use more than one pathway to grow. The presence of a mutation also does not tell us exactly how long a treatment will work for one individual.

Your care team will consider the exact alteration identified, your breast cancer subtype, previous treatments and how long they controlled the cancer, where the cancer is located and how quickly it is progressing, your overall health, any diabetes or prediabetes, possible medication interactions, side effects and quality-of-life priorities, and available clinical trials.

Side effects

What side effects should patients know about?

The PAM pathway is involved in normal functions throughout the body, including blood sugar regulation, cell growth, and metabolism. Blocking the pathway can therefore affect healthy cells as well as cancer cells. Side effects vary by medication, dose, treatment combination, and individual health.

Having diabetes or prediabetes does not always mean a pathway inhibitor cannot be used. It may simply mean that additional planning, monitoring, or support from an endocrinologist is needed.

Managing side effects is part of treatment

Side-effect management is not an afterthought — it is part of receiving cancer treatment safely. Addressing symptoms early may help prevent complications, reduce interruptions, and make it easier to stay on a treatment when it is helping.

Beyond metastatic disease

Does the PAM pathway matter in early-stage breast cancer?

The pathway can be present and biologically important in early-stage breast cancer, but most established PAM-targeted treatment uses currently apply to locally advanced or metastatic disease. Finding a PIK3CA, AKT1, or PTEN alteration in an early-stage tumor does not automatically mean a PAM pathway inhibitor should be added. Researchers continue to study whether these medicines could help prevent recurrence or improve outcomes earlier — and clinical trials are necessary to determine whether a treatment is both safe and beneficial in a new setting.

What about triple-negative or HER2-positive breast cancer?

PAM pathway alterations can also occur in triple-negative and HER2-positive breast cancers. However, finding an alteration does not necessarily mean one of the currently approved PAM-targeted treatments is appropriate. Researchers are studying pathway inhibitors across subtypes and in combination with chemotherapy, HER2-targeted therapies, endocrine therapy, immunotherapy, and other targeted treatments. A clinical trial may be an option for some patients whose tumor has a pathway alteration but who don’t meet the criteria for an existing FDA-approved treatment.

How might targeting the pathway improve outcomes?

Biomarker testing may reveal a specific alteration that can be targeted with an available medication. Blocking the PAM pathway may help interrupt one of the routes cancer cells use to keep growing despite endocrine therapy. For some patients, combining endocrine therapy with a targeted treatment may help control cancer longer than endocrine therapy alone.

What this means for you

The bottom line

The science behind the PAM pathway is complex, but its relevance is practical: it may help explain why a cancer is growing, why a previous treatment is no longer working, and whether another treatment could target a specific feature of the tumor.

Most importantly, you deserve more than a list of unfamiliar letters on a laboratory report. Ask your oncology team to walk you through what was found, what was not found, and whether the results change your options. Understanding the science does not mean carrying these decisions alone — it means having the information you need to participate meaningfully in your care.