Diagnostic BRCA Testing
Sep 10, 2026
Diagnostic BRCA Testing: What It Means If You've Already Been Diagnosed With Cancer
Quick answer: Diagnostic BRCA testing is used to find out whether someone who has already been diagnosed with cancer carries a BRCA1 or BRCA2 mutation. Unlike predictive testing, which looks at future risk, diagnostic testing looks at the cancer you already have — and the result can directly shape which treatments are likely to work best for you.
If you've been asked to consider this test, it can feel like one more decision on top of an already overwhelming diagnosis. But this test isn't about adding uncertainty — it's about giving your care team sharper tools to treat your specific cancer.
What Is the Purpose of Diagnostic BRCA Testing?
Diagnostic testing identifies whether someone who has already been diagnosed with cancer carries a BRCA mutation. This matters for two reasons:
- It can influence treatment options. Some targeted therapies are specifically more effective in patients with BRCA mutations.
- It offers insight into how the cancer may behave, helping your oncology team plan care around your specific biology, not just your cancer type.
Who Should Consider Diagnostic BRCA Testing?
Diagnostic testing is generally recommended for individuals diagnosed with:
- Breast cancer
- Ovarian cancer
- Pancreatic cancer
- Prostate cancer
It's especially relevant if you were diagnosed at a young age or have a family history of these cancers, both of which raise the likelihood that a BRCA mutation is playing a role.
How Does the Diagnostic BRCA Testing Process Work?
1. Genetic counseling. As with predictive testing, you'll typically meet with a genetic counselor first to discuss your diagnosis and what a BRCA test result could mean for your specific situation.
2. Sample collection and testing. A blood or tissue sample is collected and examined in a lab for BRCA mutations.
3. Results and follow-up. Your genetic counselor will walk you through what your result means and what to consider next.
What Do Diagnostic BRCA Test Results Mean?
A Positive Result
A positive result means a BRCA mutation is present. This can directly inform treatment decisions — for example, certain targeted therapies tend to be more effective in patients whose cancer is linked to a BRCA mutation.
A Negative Result
A negative result means no BRCA mutation was found. This can still shape your care: it may influence which treatment options your team pursues and help assess your risk of developing additional primary cancers down the line.
Diagnostic vs. Predictive BRCA Testing: What's the Difference?
It's easy to confuse the two, but they answer different questions:
| Predictive Testing | Diagnostic Testing | |
|---|---|---|
| Who it's for | People without a cancer diagnosis | People already diagnosed with cancer |
| What it assesses | Future cancer risk, often based on family history | How a current cancer may behave and respond to treatment |
| Main use | Informing screening and prevention decisions | Informing treatment strategy |
In both cases, genetic counseling is essential — it helps you understand what your result actually means and make informed decisions about your health and next steps.
If you haven't been diagnosed with cancer but have a family history of BRCA-related cancers, predictive testing may be the more relevant option. Read our guide on what a positive BRCA test result means to learn how that process works.
What Happens After You Get Your Results?
- Risk management planning. Your genetic counselor will discuss appropriate strategies based on your results, which may include enhanced surveillance, lifestyle adjustments, or preventive surgeries.
- Support resources. They can also connect you with support groups and resources for navigating the implications of your result, whether positive or negative.
Making the Decision to Test
Testing for a BRCA mutation after a cancer diagnosis is a significant decision that deserves careful consideration, counseling, and follow-up. Working closely with your healthcare team ensures you get the guidance you need to understand your options and make informed choices about your treatment and long-term health.
Frequently Asked Questions
What is diagnostic BRCA testing?
Diagnostic BRCA testing checks whether someone already diagnosed with cancer carries a BRCA1 or BRCA2 mutation, which can help guide treatment decisions.
How is diagnostic testing different from predictive testing?
Predictive testing looks at future cancer risk in people without a diagnosis, usually based on family history. Diagnostic testing looks at an existing cancer diagnosis to help determine the best treatment approach.
Who should consider diagnostic BRCA testing?
It's typically recommended for people diagnosed with breast, ovarian, pancreatic, or prostate cancer, especially if they were diagnosed young or have a family history of these cancers.
Does a positive result change my treatment plan?
It can. Certain targeted therapies tend to work more effectively in patients with a BRCA mutation, so a positive result may open up additional treatment options.
What does a negative result mean for my treatment?
A negative result means no BRCA mutation was found. It can still inform your care team's approach and help assess your risk of future primary cancers.
This article is intended for general educational purposes and is not a substitute for personalized medical advice. Please speak with a genetic counsellor or your oncology care team about your specific diagnosis and testing options.
