Breast cancer tests: what is prescribed?

When breast cancer is suspected, patients and their families often ask the same question: "What test accurately detects cancer?" Modern oncology provides a fairly definitive answer. No blood test alone confirms breast cancer. Only a biopsy followed by microscopic examination of the tissue provides definitive confirmation of the diagnosis. Therefore, discussions about "breast cancer tests" should begin not with serum tumor markers, but with morphological confirmation of the tumor. [1]

Once a malignancy is confirmed, the task changes dramatically. The doctor then needs to determine what type of tumor it is, how quickly it's growing, whether it's sensitive to hormonal therapy, whether there are targets for targeted therapy, whether a search for a hereditary mutation is necessary, and whether additional molecular testing is beneficial. In other words, modern breast cancer testing is no longer a matter of "is there cancer?" but rather a precise biological diagnosis. [2]

It's also important to understand that some tests are needed for almost all patients, while others are only needed for certain subtypes, stages, or clinical scenarios. For example, estrogen receptors, progesterone receptors, and HER2 are basic tissue biomarkers. However, multigene expression panels, PIK3CA or ESR1 mutation screening, and liquid biopsy are not necessary for every patient. A mistake here leads either to undertesting or unnecessary expenses and diagnostic noise. [3]

It's worth noting that breast cancer is not a single disease, but a group of biologically distinct tumors. According to the World Health Organization, early detection and prompt treatment reduce mortality, and some hereditary forms are associated with mutations in BRCA1, BRCA2, and PALB2. Therefore, modern testing should not simply detect the presence of a tumor, but also help classify it into the correct risk group and select the appropriate treatment strategy. [4]

A practical article on this topic should answer five questions: What confirms the diagnosis? What tissue tests are required? What blood tests are needed and why? When are genetic and molecular tests indicated? Which popular tests are overrated and should not be used as a primary guide? This is the logic behind the material below. [5]

The table below shows the main division of analyses by clinical task. [6]

Research Group	The main goal	When is it needed?
Biopsy and morphology	Confirm cancer	In case of a suspicious lesion
Tissue biomarkers	Determine tumor subtype and sensitivity to treatment	Almost everyone after the diagnosis is confirmed
Complete blood count and biochemistry	Assess the general condition and safety of therapy	Before and during treatment
Multigene panels	Clarify the risk of relapse and the benefits of chemotherapy	In some patients with early hormone-dependent HER2-negative cancer
Hereditary testing	Identify a congenital predisposition	According to modern clinical indications
Molecular analysis of a widespread tumor	Find targets for targeted or immune therapy	More common in locally advanced or metastatic disease

Sources for the table: National Cancer Institute, American Cancer Society, ASCO guidelines, and the Society of Surgical Oncology. [7]

What studies actually confirm breast cancer?

The first stage almost always begins not with testing, but with suspicion. This could be a lump detected during self-examination, a change in the shape of the breast, skin retraction, bloody discharge from the nipple, or a suspicious lesion detected on mammography, ultrasound, or magnetic resonance imaging. But even a very characteristic imaging pattern is not a definitive diagnosis. It merely provides the basis for tissue sampling. [8]

The US National Cancer Institute emphasizes that a biopsy is the only reliable way to confirm breast cancer. During a biopsy, a doctor obtains cells or tissue fragments from a suspicious area, after which a pathologist examines the material under a microscope. This is crucial: without tissue, there is no complete diagnosis, and without a complete diagnosis, it is impossible to effectively discuss treatment. [9]

In clinical practice, core biopsy, which involves collecting tissue cores with a thick needle, is most commonly used. It is considered the primary method because it provides not just individual cells, but also tissue architecture, allowing for the determination of invasiveness, histological type, and subsequent immunohistochemical and molecular studies. Fine-needle aspiration can be useful in certain situations, but as a sole method for primary tumor characterization, it is more limited. [10]

If axillary lymph node involvement is suspected, a biopsy may be performed there as well. The American Cancer Society notes that enlarged lymph nodes can be aspirated with a needle prior to surgery, and the presence of metastases in them influences the stage of the disease and subsequent treatment plan. This is important because breast cancer testing involves not only examining the tumor itself but also assessing the extent of the disease. [11]

Thus, the most important practical conclusion is simple: a diagnosis of breast cancer is made not by a tumor marker, not by a complete blood count, and not by a single image, but by a biopsy. All subsequent tests either clarify the tumor's biology, assess risk, or help select therapy. This is why a good diagnostic pathway always begins with a properly performed tissue sample. [12]

The table below shows the differences between the main types of biopsy.[13]

Type of biopsy	What do they get?	Strong point	Limitation
Fine needle aspiration	Cells or fluid	Minimally invasive, fast	Less information about tissue structure
Trephine biopsy	Fabric columns	The best material for morphology and biomarkers	A little more invasive
Surgical biopsy	Part of the hearth or the entire hearth	Full volume of fabric	Used less frequently as a first step
Lymph node biopsy	Tissue or cells from a node	Helps to estimate the spread	It solves a specific problem and does not replace a biopsy of the tumor itself.

Sources for table: US National Cancer Institute and American Cancer Society. [14]

What must be included in a pathological report?

After a biopsy, the doctor receives not just the word "cancer," but a complete pathological report. It describes the histological type of the tumor, its degree of differentiation, signs of invasion, sometimes lymphovascular invasion, the status of the resection margins if surgery has already been performed, and the condition of the lymph nodes. This report forms the basis for all subsequent treatment. If it is incomplete, the oncologist has literally nothing to rely on. [15]

One of the central parameters is the degree of malignancy, or grade. The US National Cancer Institute explains that grade reflects how atypical the cells appear and how quickly the tumor is likely to grow and spread. Three grades are typically distinguished. Grade 1 corresponds to slower-growing and more normal-looking cells, while grade 3 corresponds to more aggressive and atypical cells. [16]

The next important step is staging. The full stage is based not only on tissue but also on tumor size, lymph node status, the presence or absence of distant metastases, and some biomarkers. The American Cancer Society emphasizes that staging takes into account the T category, N category, M category, grade of malignancy, and receptor status. This further demonstrates that testing and staging are closely linked today. [17]

If surgery is performed, the resection margins are additionally assessed. Positive margins indicate that tumor cells have reached the edge of the removed tissue, which may require additional treatment. Lymph node examination, especially sentinel nodes, is also important. If the sentinel node is free of tumor, the likelihood of significant involvement of the remaining nodes is lower, and if micrometastases are present, the stage and sometimes the treatment strategy are modified. [18]

A good pathology report is not a formality, but a document that determines whether chemotherapy is needed, whether hormonal therapy is possible, whether anti-HER2 treatment is beneficial, what the risk of recurrence is, and whether further testing is needed. Essentially, pathology transforms a "suspected cancer" into a structured diagnosis that can be addressed in a meaningful way. [19]

The table below shows which parameters in the conclusion are especially important. [20]

Parameter	What does it show?	Why is it important?
Histological type	What cells does a tumor consist of?	Affects the forecast and tactics
Degree of malignancy	How aggressive does the tumor look?	Helps assess the risk of growth and spread
Tumor size	Volume of the primary lesion	Participates in staging
Lymph nodes	Is there a regional spread?	Affects the stage and extent of treatment
Resection margins	Is there any tumor left at the edge of the removed tissue?	Important for the decision on retreatment
Lymphovascular invasion	Have the cells penetrated the vessels?	Additional prognostic factor

Sources for table: American Cancer Society and National Cancer Institute. [21]

Essential tissue biomarkers: estrogen receptors, progesterone receptors, HER2, and Ki-67

After diagnosis, almost all patients require testing for baseline tissue biomarkers. The American Cancer Society recommends that all breast cancer cases be tested for estrogen receptors and progesterone receptors, and all invasive tumors for HER2. This is no longer an optional extra, but a standard of modern diagnostic testing. [22]

Estrogen receptors and progesterone receptors indicate whether a tumor is responsive to hormonal stimulation. If a tumor is positive for these receptors, the likelihood of benefit from hormonal therapy is significantly higher. The American Cancer Society notes that hormone receptor-positive tumors generally have a more favorable prognosis and are much more likely to respond to endocrine treatment than tumors without these receptors. [23]

HER2 is another type of biomarker. It reflects the presence of excess production of human epidermal growth factor receptor 2. HER2-positive tumors typically behave more aggressively but also respond significantly better to drugs directed against this target. The American Cancer Society emphasizes that all invasive tumors should be tested for HER2 in either biopsy material or surgical specimens. [24]

HER2 is typically assessed initially by immunohistochemistry. A result of 0 or 1+ is interpreted as negative, 3+ as positive, and a result of 2+ requires clarification by in situ hybridization, most often fluorescent. The College of American Pathologists also emphasizes a modern nuance: it is important to indicate a semiquantitative assessment of 0, 1+, 2+, or 3+ in the report, rather than limiting it to a general statement, because in metastatic disease, results of 1+ and 2+ without amplification can have therapeutic value. However, a special distinction of the "HER2-low" category as a mandatory separate diagnostic class is not required. [25]

Ki-67 reflects the proportion of actively dividing cells. Higher values generally indicate greater tumor proliferative activity. However, it is not a standalone "magic" test. It is interpreted only in conjunction with morphology, receptor status, HER2, and clinical presentation. Therefore, Ki-67 is useful, especially in borderline cases, but it does not replace morphology, multigene panels, or a full clinical discussion. [26]

The table below helps to quickly understand the meaning of essential tissue biomarkers. [27]

biomarker	What does a positive result mean?	What is it for?
Estrogen receptor	The tumor is dependent on estrogen stimulation	Assessment of sensitivity to hormonal therapy
Progesterone receptor	Confirms the hormonal sensitivity of the tumor	Clarification of biology and prognosis
HER2	There is excess HER2 or gene amplification	Choice of anti-HER2 therapy
Ki-67	High proportion of dividing cells	Assessment of proliferative activity
PD-L1	May be significant in some triple-negative advanced cancers	Selection of immunotherapy in appropriate cases

Sources for table: American Cancer Society, College of American Pathologists. [28]

Blood tests: Why are they needed and why don't they confirm cancer?

One of the most common myths is that breast cancer can supposedly be detected with a simple blood test. This is untrue. The American Cancer Society clearly states that blood tests are not used to diagnose breast cancer. Their role is different: to assess overall health, readiness for surgery or drug treatment, and then to monitor the patient's tolerance to therapy. [29]

A complete blood count (CBC) is important primarily as a baseline and as a monitoring tool during treatment. It reveals the presence of anemia, thrombocytopenia, leukopenia, and neutropenia. These parameters do not indicate whether cancer is present or not, but they are critical for the safety of chemotherapy, assessing the risk of bleeding and infection, and deciding whether the next treatment cycle can be started on time. [30]

A blood biochemistry test also doesn't diagnose cancer per se, but it does help assess liver, kidney, and bone function. Elevated calcium and alkaline phosphatase levels may indirectly suggest bone involvement, while changes in liver enzymes may indicate possible liver involvement or drug toxicity. However, all of these changes are nonspecific and do not, by themselves, prove the presence of metastases. They only suggest the need for further investigation. [31]

Serum tumor markers—carcinoembryonic antigen, CA 15-3, and CA 27-29—require special consideration. Current sources emphasize that they should not be used as a standalone diagnostic or monitoring tool. Their levels can be normal even in the presence of cancer and elevated in non-cancerous conditions. Therefore, relying on them as the primary test for initially suspected breast cancer is not recommended. [32]

In some cases of metastatic disease, these markers can be used as additional guidance, but only in conjunction with clinical presentation and imaging. The word "additional" is crucial. If a tumor marker rises, it doesn't always indicate progression. If it's normal, it doesn't rule out active disease. For the patient, this is perhaps one of the most useful practical ideas in this entire topic. [33]

The table below shows how to properly interpret blood tests. [34]

Blood test	What does it show?	What it doesn't show
Complete blood count	Anemia, leukopenia, thrombocytopenia, treatment tolerance	Does not confirm breast cancer
Blood biochemistry test	Liver and kidney function, indirect signs of complications	Does not determine the tumor type
Calcium, alkaline phosphatase	Possible indirect changes in bone lesions	They do not diagnose metastases on their own
Carcinoembryonic antigen	Sometimes used as an additional marker in dynamics	Not suitable for primary diagnostics
CA 15-3 and CA 27-29	Sometimes they help with metastatic disease as an adjunct	Not suitable for screening and self-monitoring

Sources for table: American Cancer Society. [35]

Multigene panels and hereditary testing: who really needs them?

Once the diagnosis is confirmed and baseline tissue biomarkers are determined, some patients face the question of whether chemotherapy is necessary if the tumor is hormone-dependent and HER2-negative. This is where multigene expression panels come into play. The National Cancer Institute and the American Cancer Society indicate that tests such as Oncotype DX, MammaPrint, Prosigna, and Breast Cancer Index are used in certain clinical scenarios to predict the risk of recurrence and guide postoperative therapy. [36]

It's crucial that these tests don't provide a diagnosis or replace morphology. They don't answer the question "is it cancer?" They answer another question: how high is the risk of disease recurrence and how likely is the benefit of chemotherapy or extended endocrine treatment. Therefore, ordering such a panel for any suspicious nodule or before biopsy confirmation is pointless. These tests confirm an established diagnosis, and only for certain subtypes. [37]

Hereditary testing is a separate area. The World Health Organization reminds that BRCA1, BRCA2, and PALB2 are highly penetrant genes that increase the risk of breast cancer. However, the modern clinical approach goes beyond the simple phrase "if there is a family history." The 2024 ASCO and Society of Surgical Oncology guidelines recommend offering BRCA1 and BRCA2 testing to all patients with newly diagnosed breast cancer under age 65, and to some patients over age 65 if they have relevant clinical factors. [38]

This shift is important not only for assessing the risk of relatives. Genetic testing results can also influence the patient's own treatment: the discussion of surgical options, preventative interventions, and, in cases of advanced HER2-negative disease, the possibility of using polyADP-ribose polymerase inhibitors. Therefore, genetic testing has ceased to be solely a family counseling tool and has become part of personalized oncology. [39]

It's important to remember the limitations of these methods. Not everyone needs a multi-gene expression panel. Not every extensive genetic testing leads to a useful clinical decision. Variants of uncertain significance should not automatically change clinical decisions. Therefore, both multi-gene panels and hereditary testing make sense when their results will actually impact treatment choices, the scope of preventative measures, or family testing. [40]

The table below separates two often confused groups of tests.[41]

Test	What does it explore?	The main question
Multigene expression panel	Gene activity in the tumor itself	Is chemotherapy necessary, what is the risk of relapse?
BRCA1, BRCA2 and other inherited genes	Congenital genetic predisposition	Is there a hereditary risk and does this affect treatment?
Oncotype DX	21 tumor genes	Benefit of chemotherapy in some early cases
MammaPrint	70 tumor genes	Risk of disease recurrence
Breast Cancer Index	11 tumor genes	Risk of late recurrence and the benefits of prolonging hormonal therapy

Sources for the table: National Cancer Institute, American Cancer Society, ASCO guidelines, and the Society of Surgical Oncology. [42]

Molecular testing in advanced disease and the role of liquid biopsy

When it comes to locally advanced or metastatic breast cancer, the range of tests expands. Here, the goal is to find targets for targeted therapy and immunotherapy. The American Cancer Society indicates that in this situation, PD-L1, PIK3CA, AKT1, PTEN, ESR1, BRCA1, BRCA2, microsatellite instability, mismatch repair defects, high mutational load, and NTRK may be examined. However, even here, tests are not selected "just in case," but based on the clinical logic of the tumor subtype and possible treatment. [43]

For triple-negative advanced cancer, PD-L1 may be important. If this protein is expressed at sufficient levels, it may support the decision to add immunotherapy to chemotherapy. For hormone-dependent HER2-negative advanced cancer, mutations in PIK3CA, AKT1, PTEN, and ESR1 are important, as they can alter sensitivity to endocrine therapy and open the way to targeted treatment options. [44]

Some of these changes can be detected not only in tissue but also in the blood using circulating tumor deoxyribonucleic acid. This is called a liquid biopsy. The American Cancer Society writes that if tissue sample volume is insufficient, some molecular tests can be performed on blood, and the ESR1 mutation, for example, can be determined from a blood sample. This makes liquid biopsy particularly useful in the dynamic analysis of advanced disease. [45]

However, liquid biopsy has very important limitations. It does not replace conventional tissue biopsy for initial diagnosis. It should not replace morphology, receptor determination, or standard HER2 diagnostics when complete tissue material is needed. Furthermore, according to recommendations from the European Society for Medical Oncology, the use of circulating tumor deoxyribonucleic acid (CDNAs) assays for the detection of molecular residual disease is not currently recommended due to a lack of proven clinical benefit. [46]

In other words, liquid biopsy is a useful modern tool, but it's not a universal answer to all questions. Its strengths include minimal invasiveness, the ability to repeat tests, and the detection of some acquired mutations during progression. Its weaknesses include the risk of false-negative results with low tumor burden and the inability to replace full-fledged tissue diagnostics where it's critical. This balanced approach is considered the most appropriate today. [47]

The table below summarizes the most important molecular tests for common disease.[48]

Test	When it is especially important	What can change
PD-L1	Triple-negative locally advanced or metastatic cancer	The possibility of immunotherapy
PIK3CA	Hormone-dependent HER2-negative advanced cancer	Selection of targeted therapy
AKT1 and PTEN	The same group of tumors	Additional targeting options
ESR1	Endocrine-resistant hormone-dependent advanced cancer	Selecting a further hormonal strategy
BRCA1 and BRCA2	HER2-negative advanced disease and hereditary risk	The possibility of therapy with polyADP-ribose polymerase inhibitors
MSI, dMMR, TMB, NTRK	More rare but clinically significant situations	Selection of individual targeted and immune drugs

Sources for table: American Cancer Society and National Cancer Institute. [49]

What does a practical patient route look like?

In simple terms, the patient's pathway for suspected breast cancer looks like this: First, imaging and clinical evaluation. Then, a biopsy. Then, pathological confirmation of the diagnosis. Then, mandatory tissue biomarkers. And only then is the decision made on additional tests, which depend on the subtype, stage, and treatment goal. This order helps avoid chaos and unnecessary testing. [50]

In early breast cancer, the primary assessment factors are typically morphology, grade, lymph node status, estrogen receptors, progesterone receptors, HER2, and sometimes Ki-67. In some patients with hormone-dependent HER2-negative variants, a multigene panel is then considered to more accurately guide chemotherapy decisions. In this group, blood tests primarily help monitor treatment safety rather than confirm the diagnosis. [51]

In locally advanced and metastatic disease, the diagnostic toolkit becomes broader. Here, additional molecular testing for mutations and protein markers is essential, as the possibility of targeted and immune-based treatment depends on them. But even in this situation, the principle remains the same: first, the tissue and basic biology of the tumor, then targeted diagnostics for a specific therapeutic question. [52]

It's helpful for patients to remember three rules. 1) The most important test is a high-quality biopsy. 2) The most important initial biomarkers are estrogen receptors, progesterone receptors, and HER2. 3) Blood tumor markers alone shouldn't be reassuring or alarming. If these three concepts are understood, much of the diagnostic confusion disappears. [53]

Modern breast cancer diagnostics have become much more accurate than before, but also more complex. Therefore, a quality article on this topic should not simply list the names of tests, but explain their hierarchy. First, diagnosis confirmation. Then subtype. Then risk. Then treatment choice. This approach allows us to transform a long list of tests into a clear and manageable action plan. [54]

FAQ

Can breast cancer be detected by a blood test?
No. Routine blood tests and serum tumor markers do not confirm breast cancer. The diagnosis is confirmed only by a biopsy with morphological examination of the tissue. [55]

What test is considered the most important after diagnosis?
The first mandatory test after a biopsy is the determination of estrogen receptors, progesterone receptors, and HER2. These data largely determine the biological subtype of the tumor and the direction of systemic treatment. [56]

Why is Ki-67 needed?
Ki-67 shows how actively tumor cells are dividing. It helps assess proliferative activity and sometimes clarifies risk, but it should not be interpreted in isolation without morphology, receptor status, and HER2. [57]

Do all patients need multigene panels?
No. These tests are only needed in certain clinical situations, most often in early hormone-dependent HER2-negative cancer, when it is necessary to clarify the risk of recurrence and the benefit of chemotherapy. They are not used for primary diagnosis. [58]

Do everyone need the CA 15-3 and CA 27-29 tumor markers?
No. They are not suitable for primary diagnosis and should not be used as a standalone monitoring criterion. They are sometimes used as an additional guideline in metastatic disease, but only in conjunction with clinical and imaging studies. [59]

When is genetic testing indicated?
According to current recommendations, BRCA1 and BRCA2 testing should be offered to all patients with newly diagnosed breast cancer under the age of 65, and to some patients over 65, depending on their medical history, origin, and the potential impact of the results on treatment. [60]

What is a liquid biopsy and does it replace a standard biopsy?
A liquid biopsy is a test that looks for tumor deoxyribonucleic acid in the blood. It can be useful in advanced disease to look for certain mutations, such as ESR1, but it does not replace a standard tissue biopsy for initial diagnosis. [61]

Should PD-L1 be measured in all patients?
No. This marker is primarily important for some patients with triple-negative locally advanced or metastatic cancer when immunotherapy is being considered. For most early hormone-dependent tumors, it is not included in the basic mandatory test set. [62]