Evaluating and Understanding Breast Cancer Studies

For 42 years, breast cancer researchers and doctors have been gathering in San Antonio every year to review the latest research at the eponymous San Antonio Breast Cancer Symposium (SABCS). Thousands of people from countless subspecialties each bring their unique lens to a disease that affects increasing numbers of people around the world. It’s a big conference with a lot of information. And it’s full of dense insider speak – which reminds me that I once heard that obscure medical terminology was developed at a time when doctors routinely kept patients in the dark about their conditions.

Over the years more patient advocates have come to SABCS, but most of us don’t have backgrounds in medicine, biology, oncology, epidemiology, or other related fields. Sometimes people ask me to explain the alphabet soup of acronyms and medical terms that are commonly used by SABCS presenters and participants.

In order to fully understand the data presented at SABCS, it’s helpful to understand the different endpoints that get used in breast cancer trials—endpoints being what’s measured in a particular trial. Different endpoints tell us different things about the effectiveness of experimental breast cancer treatments.

The number one way most people judge a cancer treatment is if it helps them live longer, that is, if it improves survival. But that’s not always what researchers study and so it can be hard to know what different kinds of data really means for patients. I created a Twitter thread to help explain commonly used endpoints that are the primary outcomes measured by a clinical trial, and it got so much positive response, I thought I’d share it here, too.

Clinical endpoints are outcomes that demonstrate direct benefit to patients and include things like survival, the absence of disease, and decreased pain. Survival is a paramount clinical endpoint for most people with breast cancer and may be studied in different ways.

• Overall survival (OS) is length of time someone is still alive from either the date of diagnosis or the start of treatment.
• Disease-free survival (DFS) is the period after treatment during which no sign of cancer is found.
• Progression-free survival (PFS) is the length of time during and after treatment that a patient lives with the disease but it does not get worse.

Because survival data can take a long time, making a study expensive, surrogate endpoints are often used as a substitute for clinical endpoints, providing an intermediate measure of the likely effects of a specific treatment. Surrogate endpoints are meaningful for researchers and may provide useful indication that the research hypothesis is on track, but they do not always correlate with real clinical endpoints that benefit patients.

• Progression-free survival (PFS) is the length of time during and after treatment that the cancer doesn’t progress/get worse.
• Objective response rate (ORR) is the percent of patients whose cancer shrinks or disappears after treatment.
• Pathological complete response (pCR) is the complete disappearance of the cancer after treatment with systemic therapy before surgery.

From the patient side, most people want to know they don’t have cancer after treatment.

• No evidence of disease (NED) means the cancer can’t be found on imaging tests after treatment (this is also called complete remission or complete response). Because the cancer may recur, NED doesn’t mean the cancer is cured.