Breast Cancer
A comprehensive, plain-language guide to breast cancer — types, staging, biomarkers, treatment options, side effects, and questions to ask your doctor.
Quick Overview
In This Guide
What Is Breast Cancer?
Breast cancer is a disease in which cells in the breast begin to grow out of control. Normally, your body creates new cells to replace old or damaged ones in an orderly process. Cancer disrupts that process. Instead of dying when they should, abnormal cells keep multiplying, eventually forming a mass called a tumor. Not all tumors are cancer — benign tumors are not life-threatening and do not spread to other parts of the body — but malignant tumors can invade nearby tissue and, if untreated, can spread (metastasize) to other organs.
To understand breast cancer, it helps to know the basic anatomy. The breast is made up of three main types of tissue: lobules (the glands that can produce milk), ducts (the tiny tubes that carry milk from the lobules to the nipple), and connective tissue (fibrous and fatty tissue that surrounds and holds everything together). Most breast cancers begin in the cells lining the ducts (ductal cancers) or in the lobules (lobular cancers). The connective tissue, blood vessels, and lymph vessels in the breast can also be involved as the cancer progresses.
Breast cancer is not a single disease. It is a group of diseases with different molecular profiles, behaviors, and treatment responses. Two people with "breast cancer" may have very different diagnoses, prognoses, and treatment plans. This is why understanding your specific pathology report — your tumor type, grade, stage, and biomarkers — is so important. It is the foundation of your personalized treatment plan.
Types of Breast Cancer
Breast cancer is classified by where it starts, whether it has spread, and its molecular characteristics. Here are the major types.
Invasive Ductal Carcinoma (IDC)
IDC is the most common type of breast cancer, accounting for approximately 70-80% of all diagnoses. It begins in the cells lining the milk ducts and then breaks through the duct wall to grow into the surrounding breast tissue. From there, it has the potential to spread to lymph nodes and other parts of the body. IDC can occur at any age but is most common in women over 55.
Invasive Lobular Carcinoma (ILC)
ILC accounts for about 10-15% of invasive breast cancers. It starts in the milk-producing lobules and spreads into surrounding breast tissue. ILC tends to grow in a single-file pattern, which can make it harder to detect on mammograms. It is more likely to occur in both breasts compared to other types and is often hormone receptor positive.
Ductal Carcinoma In Situ (DCIS)
DCIS is a non-invasive condition in which abnormal cells are found in the lining of a breast milk duct but have not spread outside the duct into surrounding breast tissue. It is sometimes called "Stage 0" breast cancer. While DCIS itself is not life-threatening, it can increase the risk of developing invasive breast cancer later if left untreated. Treatment usually involves surgery and sometimes radiation.
Inflammatory Breast Cancer (IBC)
IBC is a rare and aggressive form of breast cancer that accounts for 1-5% of cases. Unlike other types, it often does not produce a distinct lump. Instead, cancer cells block lymph vessels in the skin of the breast, causing the breast to appear swollen, red, and warm — resembling an infection. The skin may look pitted like an orange peel. IBC tends to grow and spread quickly and requires prompt, aggressive treatment.
Triple-Negative Breast Cancer
Triple-negative breast cancer (TNBC) tests negative for estrogen receptors (ER-), progesterone receptors (PR-), and HER2 protein (HER2-). This means it does not respond to hormonal therapy or HER2-targeted therapy. TNBC accounts for about 10-15% of breast cancers and tends to be more aggressive. It is more common in younger women and women with BRCA1 mutations. Treatment typically involves chemotherapy, and newer immunotherapy options are expanding.
HER2-Positive Breast Cancer
HER2-positive breast cancer overproduces the HER2 (human epidermal growth factor receptor 2) protein, which promotes cancer cell growth. About 15-20% of breast cancers are HER2-positive. Before targeted therapies were developed, HER2-positive cancers had a poorer prognosis. Today, drugs like trastuzumab (Herceptin) and other HER2-targeted therapies have dramatically improved outcomes, making this one of the most treatable subtypes.
Symptoms & Early Signs
Breast cancer symptoms vary from person to person. Some people have no symptoms at all and the cancer is found on a screening mammogram. When symptoms do appear, they may include the following.
Diagnosis & Testing
Diagnosing breast cancer usually involves several steps. Here is what to expect, from the initial evaluation through the final pathology report.
Clinical Breast Exam
Your doctor physically examines your breasts, checking for lumps, skin changes, nipple abnormalities, and lymph node swelling in the underarm and collarbone areas. This is often the first step after a symptom is reported or an abnormality is found on screening.
Mammogram & Ultrasound
A diagnostic mammogram takes detailed X-ray images of the breast from multiple angles. If the mammogram shows a suspicious area, or if you have dense breast tissue, an ultrasound may be performed to determine whether a mass is solid (possibly cancerous) or fluid-filled (usually a benign cyst). Both are non-invasive and generally take less than 30 minutes.
Biopsy
A biopsy is the only definitive way to diagnose breast cancer. A small sample of tissue is removed and examined under a microscope by a pathologist. The most common type is a core needle biopsy, which uses a hollow needle to extract small cylinders of tissue. In some cases, an excisional biopsy (surgical biopsy) may be performed to remove the entire suspicious area. The procedure is usually done with local anesthesia and image guidance.
Pathology Report
After the biopsy, a pathologist examines the tissue and produces a pathology report. This document contains critical information about your cancer, including the type of cancer, the grade (how abnormal the cells look), hormone receptor status (ER, PR), HER2 status, and surgical margins if tissue was removed. This report is the blueprint for your treatment plan.
Additional Imaging (If Needed)
Depending on your diagnosis, your doctor may order additional tests to determine the extent of the cancer. These can include a breast MRI for a more detailed view of the breast, a CT scan to check whether cancer has spread to other organs, a bone scan to check the bones, or a PET scan which highlights metabolically active cancer cells throughout the body.
Staging
Staging describes how far the cancer has spread. Breast cancer is staged using the TNM system, which considers three factors: the size of the tumor (T), whether cancer has reached nearby lymph nodes (N), and whether it has metastasized to distant organs (M).
The TNM System
T — Tumor Size
- T1: Tumor is 2 centimeters (cm) or smaller. This is roughly the size of a peanut or smaller. T1 is further divided into T1a (larger than 1mm but not larger than 5mm), T1b (larger than 5mm but not larger than 10mm), and T1c (larger than 10mm but not larger than 20mm).
- T2: Tumor is larger than 2 cm but not larger than 5 cm. Approximately the size of a grape to a lime.
- T3: Tumor is larger than 5 cm. Approximately the size of a lime or larger.
- T4: Tumor of any size that has grown into the chest wall or skin. This includes inflammatory breast cancer (T4d).
N — Lymph Node Involvement
- N0: Cancer has not spread to nearby lymph nodes.
- N1: Cancer has spread to 1-3 axillary (underarm) lymph nodes and/or tiny amounts of cancer are found in internal mammary lymph nodes on sentinel lymph node biopsy.
- N2: Cancer has spread to 4-9 axillary lymph nodes, or cancer has enlarged internal mammary lymph nodes.
- N3: Cancer has spread to 10 or more axillary lymph nodes, or to lymph nodes under the collarbone (infraclavicular), or to lymph nodes above the collarbone (supraclavicular).
M — Metastasis (Distant Spread)
- M0: No evidence that cancer has spread to distant organs.
- M1: Cancer has spread to distant organs such as the bones, lungs, liver, or brain.
Stage Groupings
Non-Invasive (DCIS)
Abnormal cells are present but confined to the duct lining. They have not invaded surrounding breast tissue. Stage 0 is highly treatable with an excellent prognosis. It is sometimes referred to as "pre-cancer," although it does require treatment to prevent potential progression to invasive cancer.
Early-Stage Invasive
The tumor is small (up to 2 cm) and cancer has either not spread to the lymph nodes or only tiny clusters of cancer cells (micrometastases) are found in the lymph nodes. Stage I breast cancer is considered early-stage and has a very high survival rate. Treatment typically involves surgery, possibly radiation, and may include systemic therapy depending on biomarkers.
Localized Spread
The tumor is between 2-5 cm and may have spread to 1-3 axillary lymph nodes, or the tumor is larger than 5 cm but has not spread to lymph nodes. Stage II is still considered early-stage cancer. Treatment usually involves a combination of surgery, radiation, and systemic therapy (chemotherapy, hormone therapy, or targeted therapy).
Locally Advanced
The tumor may be any size and cancer has spread to many nearby lymph nodes (4-9 or more), or the tumor has grown into the chest wall or skin. Stage III is also called locally advanced breast cancer. It has not spread to distant organs. Treatment is typically aggressive and multi-modal, often starting with chemotherapy before surgery (neoadjuvant chemotherapy) to shrink the tumor.
Metastatic
Cancer has spread beyond the breast and nearby lymph nodes to distant organs — most commonly the bones, lungs, liver, or brain. Stage IV breast cancer is also called metastatic breast cancer. While it is generally considered not curable, it is treatable. Many people live for years with metastatic breast cancer thanks to modern treatments. The goal of treatment shifts toward controlling the cancer, maintaining quality of life, and extending survival.
Biomarkers
Biomarkers are measurable characteristics of your cancer cells that help your oncologist choose the most effective treatment. These are determined from your biopsy tissue and reported on your pathology report.
ER (Estrogen Receptor)
The estrogen receptor test determines whether your cancer cells have receptors for the hormone estrogen. If the test is ER-positive (ER+), it means estrogen can promote the growth of your cancer. This is significant because hormone therapy drugs, which block estrogen or lower its levels, can be very effective. About 70-80% of breast cancers are ER-positive. If the test is ER-negative (ER-), estrogen is not fueling the cancer's growth, and hormone therapy will not be part of the treatment plan.
PR (Progesterone Receptor)
Similar to the estrogen receptor test, this test checks whether your cancer cells have receptors for progesterone. PR-positive (PR+) cancers are also likely to respond to hormone therapy. PR status is usually tested alongside ER status. Cancers that are both ER+ and PR+ generally have the best response to hormone therapy. Cancers that are ER+ but PR- may still benefit from hormone therapy, though the response may differ.
HER2 Status
HER2 (human epidermal growth factor receptor 2) is a protein that promotes cell growth. In about 15-20% of breast cancers, the HER2 gene is amplified, causing the cells to produce too much HER2 protein. This is called HER2-positive. These cancers tend to grow faster but respond well to targeted therapies like trastuzumab (Herceptin), pertuzumab (Perjeta), and ado-trastuzumab emtansine (T-DM1). HER2 status is determined by IHC (immunohistochemistry) testing, scored 0 to 3+. A score of 3+ is HER2-positive. A score of 2+ is considered equivocal and requires an additional FISH (fluorescence in situ hybridization) test to confirm. Recent research on "HER2-low" cancers (IHC 1+ or 2+/FISH-negative) has opened new treatment options with antibody-drug conjugates.
Ki-67 (Proliferation Rate)
Ki-67 is a protein found in cells that are actively dividing. The Ki-67 test measures the percentage of cancer cells that are in the process of growing and dividing. A high Ki-67 percentage (generally above 20%) indicates the cancer is growing quickly and may be more responsive to chemotherapy, which targets rapidly dividing cells. A low Ki-67 suggests slower growth. Ki-67 helps your oncologist determine the aggressiveness of the cancer and whether chemotherapy should be part of your treatment.
Oncotype DX & MammaPrint
Oncotype DX analyzes the activity of 21 genes in early-stage, ER-positive, HER2-negative breast cancer and produces a Recurrence Score (0-100) that predicts the likelihood of the cancer returning and the likely benefit of chemotherapy. A low score (0-25) often means chemotherapy can be safely skipped. MammaPrint is a 70-gene test that classifies cancers as low-risk or high-risk for recurrence within 10 years. Both tests help avoid unnecessary chemotherapy for patients who will not benefit from it, and identify those who will.
BRCA1 & BRCA2 Gene Mutations
BRCA1 and BRCA2 are genes that produce proteins responsible for repairing damaged DNA. When either gene is mutated, DNA damage may not be repaired properly, and cells are more likely to develop cancer. Women with a BRCA1 mutation have a 55-72% lifetime risk of developing breast cancer; those with a BRCA2 mutation have a 45-69% risk. BRCA mutations are inherited from a parent and also increase the risk of ovarian cancer. Knowing your BRCA status can influence surgical decisions (such as considering bilateral mastectomy), treatment options (PARP inhibitors are effective in BRCA-mutated cancers), and screening recommendations for your family members.
Why Biomarkers Matter
Biomarkers are not just academic details on your pathology report — they are the compass that guides your treatment. An ER-positive cancer will be treated differently from a triple-negative cancer. A HER2-positive cancer opens the door to targeted therapies that have transformed outcomes. Your biomarker profile is what makes your treatment plan uniquely yours, and it is the reason two people with the same stage of breast cancer may receive very different treatments.
Treatment Options
Treatment for breast cancer depends on the type, stage, biomarkers, and your overall health. Most treatment plans combine several approaches.
Surgery
Surgery is the primary treatment for most early-stage breast cancers. A lumpectomy (breast-conserving surgery) removes the tumor and a margin of surrounding tissue while preserving most of the breast. It is typically followed by radiation therapy. A mastectomy removes the entire breast and is recommended when cancer is large relative to breast size, multifocal, or when the patient prefers it. Sentinel lymph node biopsy checks whether cancer has spread to the first lymph nodes draining the breast. If cancer is found, more lymph nodes may be removed (axillary dissection). Breast reconstruction can be performed at the time of mastectomy (immediate) or later (delayed), using implants or tissue from another part of the body.
Radiation Therapy
Radiation therapy uses high-energy beams to destroy cancer cells remaining in the breast, chest wall, or lymph nodes after surgery. It is almost always recommended after lumpectomy and sometimes after mastectomy. External beam radiation is the most common form, typically given 5 days a week for 3-6 weeks. Accelerated partial breast irradiation delivers a higher dose to a smaller area over fewer sessions. Common side effects include skin redness, fatigue, and mild swelling in the treated area. Most side effects resolve within weeks to months after treatment ends.
Chemotherapy
Chemotherapy uses drugs to kill or slow the growth of cancer cells throughout the body. It may be given before surgery (neoadjuvant) to shrink a large tumor, or after surgery (adjuvant) to kill any remaining cancer cells. Common regimens include AC-T (doxorubicin/cyclophosphamide followed by a taxane), TC (docetaxel/cyclophosphamide), and CMF (cyclophosphamide/methotrexate/fluorouracil). Treatment is given in cycles — typically every 2-3 weeks for 3-6 months. Side effects vary but can include fatigue, nausea, hair loss, increased infection risk, and neuropathy. Supportive medications can help manage many of these effects.
Hormone (Endocrine) Therapy
For ER-positive and/or PR-positive breast cancers, hormone therapy blocks the body's hormones from fueling cancer growth. Tamoxifen blocks estrogen receptors on cancer cells and is used in both pre- and postmenopausal women, typically for 5-10 years. Aromatase inhibitors (AIs) — including letrozole (Femara), anastrozole (Arimidex), and exemestane (Aromasin) — lower estrogen levels in the body and are used in postmenopausal women for 5-10 years. Ovarian suppression may be added for premenopausal women to stop the ovaries from producing estrogen. Side effects can include hot flashes, joint pain, bone thinning, and menopausal symptoms.
Targeted Therapy
Targeted therapies are drugs designed to attack specific features of cancer cells. For HER2-positive cancers, trastuzumab (Herceptin) and pertuzumab (Perjeta) target the HER2 protein directly. Antibody-drug conjugates like ado-trastuzumab emtansine (T-DM1) and trastuzumab deruxtecan (Enhertu) deliver chemotherapy directly to HER2-expressing cells. For ER-positive cancers, CDK4/6 inhibitors — palbociclib (Ibrance), ribociclib (Kisqali), and abemaciclib (Verzenio) — have become standard additions to hormone therapy for advanced disease. PARP inhibitors like olaparib (Lynparza) are used for BRCA-mutated cancers. Targeted therapies tend to have fewer side effects than traditional chemotherapy because they are more precise.
Immunotherapy
Immunotherapy helps your immune system recognize and fight cancer cells. Pembrolizumab (Keytruda) is approved for triple-negative breast cancer that is PD-L1 positive. It is typically given in combination with chemotherapy before surgery (neoadjuvant setting) and continued after surgery. Immunotherapy works by blocking the PD-1/PD-L1 pathway that cancer cells use to hide from the immune system. Side effects can include fatigue, skin reactions, and immune-related side effects affecting the thyroid, liver, lungs, or other organs. Your oncology team will monitor for these carefully.
Side Effects & Management
Every treatment comes with potential side effects. Understanding what to expect can help you prepare, cope, and communicate with your care team. You do not have to endure side effects silently — there are strategies and medications to help manage most of them.
Fatigue
The most commonly reported side effect across nearly all breast cancer treatments. Cancer-related fatigue is different from normal tiredness — rest may not fully relieve it. Management: Gentle exercise (walking, yoga) has been shown to reduce fatigue. Prioritize sleep, pace your activities, and ask for help. Tell your doctor if fatigue is severe — it can sometimes indicate anemia or thyroid issues that are treatable.
Nausea & Vomiting
Common with chemotherapy and some targeted therapies. Management: Anti-nausea medications (antiemetics) are very effective and are routinely prescribed before and after chemotherapy. Eating small, frequent meals, avoiding strong odors, and staying hydrated can also help. Ginger and acupressure wristbands provide relief for some people.
Hair Loss (Alopecia)
Many chemotherapy regimens cause partial or complete hair loss, usually beginning 2-3 weeks after treatment starts. Hair typically regrows after chemotherapy ends, often within 3-6 months. Management: Scalp cooling caps can reduce hair loss for some patients. Many people find comfort in wigs, scarves, or hats. Some embrace the experience. There is no wrong way to handle hair loss.
Neuropathy
Peripheral neuropathy — tingling, numbness, or pain in the hands and feet — is a common side effect of taxane chemotherapy drugs (paclitaxel, docetaxel). Management: Report symptoms early, as your oncologist may adjust your dose. Ice or cold gloves/socks during infusion may help. Physical therapy, gentle exercise, and medications like gabapentin or duloxetine can provide relief. Neuropathy usually improves after treatment but can sometimes persist.
Lymphedema
Swelling in the arm or hand on the side where lymph nodes were removed or treated with radiation. It can occur weeks, months, or even years after treatment. Management: A certified lymphedema therapist can teach compression techniques, manual lymphatic drainage, and exercises. Wearing a compression sleeve during exercise or air travel may help. Report any new swelling to your doctor immediately — early treatment is most effective.
Menopausal Symptoms
Hormone therapy and ovarian suppression can cause or worsen menopausal symptoms including hot flashes, night sweats, vaginal dryness, mood changes, and decreased libido. Chemotherapy can also cause premature menopause in premenopausal women. Management: Layered clothing, cooling fans, and avoiding triggers (caffeine, alcohol, spicy food) can help with hot flashes. Vaginal moisturizers and lubricants address dryness. Talk to your oncologist about safe options — some non-hormonal medications can help.
Cognitive Changes ("Chemo Brain")
Many patients report difficulties with memory, concentration, and mental clarity during and after treatment. This is sometimes called "chemo brain" or "chemo fog," though it can also occur with hormone therapy and other treatments. Management: Use lists, calendars, and reminders. Exercise has been shown to improve cognitive function. Get adequate sleep. Cognitive rehabilitation therapy may help. Know that this is a real, recognized effect — you are not imagining it.
Emotional Impact
Anxiety, depression, fear of recurrence, grief, anger, and isolation are common throughout the cancer journey — during treatment and long after it ends. Management: Seek support from a licensed therapist or counselor experienced in oncology. Support groups (in person or online) connect you with others who understand. Mindfulness, meditation, and journaling can help. Talk to your care team — mental health is a legitimate and important part of cancer care.
Living With Breast Cancer
A breast cancer diagnosis affects every part of your life — not just your body. Here are important topics that are often overlooked but deeply matter.
Fertility Considerations
If you are of childbearing age, discuss fertility preservation before treatment begins. Some chemotherapy drugs and hormone therapies can affect your ability to become pregnant. Options include egg or embryo freezing (cryopreservation), ovarian tissue preservation, or the use of GnRH agonists to protect ovarian function during chemotherapy. Time is critical — fertility preservation procedures need to happen before treatment starts. Ask for a referral to a reproductive endocrinologist immediately after diagnosis if fertility matters to you.
Sexuality & Body Image
Breast cancer and its treatments can significantly impact body image, sexual desire, and sexual function. Surgical changes, hair loss, weight fluctuations, vaginal dryness, fatigue, and hormonal shifts can all play a role. These changes are normal and valid. Open communication with your partner (if applicable) and your healthcare team is essential. Oncology sexual health specialists can provide specific guidance. Counseling, peer support groups, and resources focused on intimacy after cancer are available and can make a meaningful difference.
Mental Health Support
The emotional toll of cancer is real and significant. It is not weakness to struggle — it is a natural response to an extraordinary situation. Depression and anxiety affect a substantial proportion of cancer patients. Professional support from a psychologist, psychiatrist, or clinical social worker experienced in oncology can be transformative. Many cancer centers have integrated mental health services. If yours does not, ask for a referral. Online therapy options have also expanded access. National helplines, including the Cancer Support Helpline (1-888-793-9355) and Crisis Text Line (text HOME to 741741), are available when you need to talk.
Work & Financial Concerns
Cancer treatment can strain finances and work life. Many patients face decisions about taking leave, reducing hours, or managing treatment around work schedules. Know your rights: in the United States, the Family and Medical Leave Act (FMLA) provides job-protected leave, and the Americans with Disabilities Act (ADA) requires employers to provide reasonable accommodations. Financial assistance programs exist through pharmaceutical companies (patient assistance programs), nonprofit organizations, and hospital financial counselors. A social worker or financial navigator at your cancer center can help you access these resources.
Survivorship Care
After active treatment ends, the journey continues. Survivorship care includes regular follow-up appointments (typically every 3-6 months for the first few years, then annually), ongoing screening mammograms, management of long-term side effects, and monitoring for recurrence. Ask your oncologist for a survivorship care plan — a written document that summarizes your diagnosis, treatments received, follow-up schedule, and potential late effects to watch for. This document helps your entire healthcare team (including your primary care doctor) coordinate your ongoing care.
Questions to Ask Your Doctor
Walking into a doctor's appointment with prepared questions can help you feel more in control and ensure you leave with the information you need. Here are questions organized by where you are in your journey.
At Diagnosis
Before Treatment
During Treatment
After Treatment
Sources & References
The information on this page is drawn from the following authoritative sources. We aim to reflect current clinical guidelines and peer-reviewed evidence. This page does not replace professional medical advice.
- American Cancer Society (ACS) — Breast Cancer Facts & Figures; Cancer Statistics 2024; Treatment Guidelines
- World Health Organization (WHO) — Global Cancer Observatory (GLOBOCAN); Breast Cancer Fact Sheet
- National Cancer Institute (NCI) — Breast Cancer Treatment (PDQ); SEER Cancer Statistics Review
- National Comprehensive Cancer Network (NCCN) — NCCN Clinical Practice Guidelines in Oncology: Breast Cancer
- American Society of Clinical Oncology (ASCO) — Patient Information Guides; Practice Guidelines
- UpToDate — Clinical Decision Support (Breast Cancer Overview, Staging, and Treatment)
Last reviewed: 2025. StopMyCancer regularly reviews and updates its content to reflect the latest clinical evidence and guidelines. If you believe any information on this page is outdated or inaccurate, please contact us.