Breast cancer is the most commonly diagnosed cancer in women worldwide and the second leading cause of cancer death among women in the United States. According to the American Cancer Society (ACS), approximately 310,000 new cases of invasive breast cancer are diagnosed in American women each year, along with about 56,000 cases of ductal carcinoma in situ (DCIS). However, death rates from breast cancer have declined steadily since 1989, largely due to improved screening, earlier detection, and advances in treatment.
Men can also develop breast cancer, accounting for roughly 1% of all breast cancer diagnoses. The information in this guide applies broadly to breast cancer treatment regardless of sex, though treatment plans are always individualized.
What Is Breast Cancer?
Breast cancer begins when cells in the breast grow out of control, typically forming a tumor that can often be detected on imaging studies or felt as a lump. Breast tissue extends from the collarbone to the underarm and across to the breastbone. The breast contains lobes (milk-producing glands), ducts (tubes that carry milk to the nipple), and stroma (fatty and connective tissue). Most breast cancers originate in the ducts or lobes.
Not all breast lumps are cancerous. Benign conditions such as fibroadenomas and cysts are common. However, any new lump or breast change should be evaluated by a healthcare provider promptly.
Types of Breast Cancer
Ductal Carcinoma In Situ (DCIS)
DCIS is a non-invasive condition in which abnormal cells are found in the lining of the breast duct but have not spread beyond the duct wall into surrounding breast tissue. DCIS is considered stage 0 breast cancer. While not life-threatening on its own, untreated DCIS can progress to invasive cancer. Treatment typically involves lumpectomy with or without radiation, and in some cases mastectomy. According to the NCI, DCIS accounts for about 20–25% of all newly diagnosed breast cancers.
Invasive Ductal Carcinoma (IDC)
IDC is the most common type of breast cancer, representing approximately 70–80% of all invasive breast cancers. It begins in the milk ducts and breaks through the duct wall to invade surrounding breast tissue. IDC can spread to lymph nodes and distant organs through the lymphatic system and bloodstream.
Invasive Lobular Carcinoma (ILC)
ILC is the second most common type, accounting for 10–15% of invasive breast cancers. It originates in the milk-producing lobules. ILC tends to grow in a single-file pattern through breast tissue, which can make it harder to detect on mammograms. It is more likely to occur in both breasts compared to IDC.
Inflammatory Breast Cancer (IBC)
IBC is a rare and aggressive form, accounting for 1–5% of breast cancers. Rather than forming a distinct lump, cancer cells block lymph vessels in the skin of the breast, causing the breast to appear swollen, red, and warm. IBC is typically classified as stage III or IV at diagnosis and requires aggressive multimodal treatment including chemotherapy before surgery (neoadjuvant chemotherapy), modified radical mastectomy, and radiation therapy.
Triple-Negative Breast Cancer (TNBC)
TNBC accounts for approximately 10–15% of all breast cancers. It tests negative for estrogen receptors, progesterone receptors, and HER2 protein, meaning it does not respond to hormone therapy or HER2-targeted drugs. TNBC is typically treated with a combination of surgery, chemotherapy, and in some cases immunotherapy. The checkpoint inhibitor pembrolizumab (Keytruda), combined with chemotherapy, received FDA approval for early-stage and metastatic TNBC with PD-L1 expression.
HER2-Positive Breast Cancer
Approximately 15–20% of breast cancers overexpress the HER2 protein, which promotes cancer cell growth. HER2-positive cancers tend to be more aggressive but respond well to HER2-targeted therapies such as trastuzumab (Herceptin), pertuzumab (Perjeta), ado-trastuzumab emtansine (T-DM1, Kadcyla), and trastuzumab deruxtecan (Enhertu). These targeted agents have dramatically improved outcomes for HER2-positive patients.
Risk Factors
Several factors can increase the risk of developing breast cancer. Having one or more risk factors does not mean a person will develop cancer, and many people diagnosed with breast cancer have no identifiable risk factors beyond being female and aging.
- Age — Risk increases with age. Most breast cancers are diagnosed in women over 50.
- Family history — Having a first-degree relative (mother, sister, daughter) with breast cancer approximately doubles the risk.
- Genetic mutations — Inherited mutations in BRCA1 and BRCA2 genes significantly increase lifetime risk (up to 72% for BRCA1 and 69% for BRCA2, according to NCI data).
- Reproductive factors — Early menstruation (before age 12), late menopause (after 55), first pregnancy after age 30, or never having a full-term pregnancy.
- Hormone replacement therapy (HRT) — Combined estrogen-progestin HRT used for more than five years increases risk.
- Dense breast tissue — Women with dense breasts have a higher risk and mammograms may be less sensitive.
- Lifestyle factors — Obesity (particularly after menopause), physical inactivity, alcohol consumption (even moderate intake), and smoking.
- Prior chest radiation — Radiation therapy to the chest area before age 30 (for example, to treat Hodgkin lymphoma) increases risk.
Breast Cancer Staging
Staging describes how far the cancer has spread and is a key factor in determining treatment. Breast cancer uses the TNM system (Tumor size, Node involvement, Metastasis) along with biomarker information (ER, PR, HER2, grade) for a more complete prognostic picture.
| Stage | Description | 5-Year Survival Rate |
|---|---|---|
| Stage 0 (DCIS) | Non-invasive; cancer cells confined to the ducts | Nearly 100% |
| Stage I | Tumor up to 2 cm, no or minimal lymph node involvement | ~99% |
| Stage II | Tumor 2–5 cm and/or spread to 1–3 axillary lymph nodes | ~93% |
| Stage III | Locally advanced; larger tumor and/or extensive lymph node involvement | ~72% |
| Stage IV | Metastatic; cancer has spread to distant organs (bones, lungs, liver, brain) | ~31% |
Survival rates based on SEER data from the National Cancer Institute. Individual outcomes vary based on cancer subtype, biomarkers, overall health, and response to treatment.
Treatment Options
Breast cancer treatment is highly individualized and depends on the cancer type, stage, biomarker status (ER, PR, HER2), genetic profile, the patient's overall health, and personal preferences. Most patients receive a combination of treatments.
Surgery
Surgery is the cornerstone of breast cancer treatment for most patients. The two primary surgical approaches are:
- Lumpectomy (breast-conserving surgery) — Removes the tumor and a margin of surrounding normal tissue while preserving the rest of the breast. Typically followed by radiation therapy. Studies show lumpectomy plus radiation produces survival rates equivalent to mastectomy for early-stage cancers.
- Mastectomy — Removes the entire breast. Options include simple (total) mastectomy, modified radical mastectomy (breast plus axillary lymph nodes), and skin-sparing or nipple-sparing mastectomy for reconstruction candidates.
Sentinel lymph node biopsy is standard practice to determine whether cancer has spread to the axillary lymph nodes, helping to avoid the side effects of full axillary lymph node dissection when nodes are clear.
Radiation Therapy
Radiation therapy uses high-energy beams to destroy remaining cancer cells after surgery. It is standard after lumpectomy and may be recommended after mastectomy for larger tumors or positive lymph nodes. Modern techniques include whole-breast irradiation, accelerated partial-breast irradiation, and hypofractionated schedules that reduce treatment from six weeks to three or four weeks. Learn more about radiation therapy.
Chemotherapy
Chemotherapy may be administered before surgery (neoadjuvant) to shrink tumors or after surgery (adjuvant) to eliminate microscopic disease. Common regimens include AC-T (doxorubicin/cyclophosphamide followed by a taxane), TC (docetaxel/cyclophosphamide), and dose-dense AC-T. Genomic assays such as Oncotype DX and MammaPrint can help predict which patients will benefit from chemotherapy, potentially sparing low-risk patients from unnecessary treatment. Learn more about chemotherapy.
Hormone (Endocrine) Therapy
Approximately 80% of breast cancers are hormone receptor-positive. Hormone therapy blocks the effects of estrogen on cancer cells or lowers estrogen production. Key medications include:
- Tamoxifen — A selective estrogen receptor modulator (SERM) used in pre- and postmenopausal women, typically for 5–10 years.
- Aromatase inhibitors (AIs) — Letrozole, anastrozole, and exemestane reduce estrogen production in postmenopausal women. Often used for 5–10 years.
- CDK4/6 inhibitors — Palbociclib (Ibrance), ribociclib (Kisqali), and abemaciclib (Verzenio) are used in combination with hormone therapy for advanced HR-positive, HER2-negative breast cancer, significantly improving progression-free survival.
HER2-Targeted Therapy
For HER2-positive breast cancers, targeted agents are a critical component of treatment. Trastuzumab (Herceptin) reduced the risk of recurrence by approximately 50% when added to chemotherapy in clinical trials. Current standard approaches include trastuzumab combined with pertuzumab (dual HER2 blockade) plus chemotherapy for both early and advanced disease. Antibody-drug conjugates such as T-DM1 and trastuzumab deruxtecan deliver chemotherapy directly to HER2-expressing cells with less systemic toxicity.
Immunotherapy
Immunotherapy has become part of treatment for triple-negative breast cancer. Pembrolizumab (Keytruda) in combination with chemotherapy is approved for early-stage TNBC (neoadjuvant and adjuvant settings) and for PD-L1-positive metastatic TNBC. Research into expanding immunotherapy to other breast cancer subtypes is ongoing.
Screening Recommendations
The ACS recommends the following breast cancer screening guidelines for women at average risk:
- Ages 40–44: Option to begin annual mammograms
- Ages 45–54: Annual mammograms recommended
- Ages 55 and older: Mammograms every 1–2 years, continuing as long as overall health is good
Women at higher risk (BRCA mutation carriers, strong family history, prior chest radiation) may benefit from starting screening earlier and adding breast MRI. View our complete screening guide.
Living with Breast Cancer
A breast cancer diagnosis affects every aspect of a patient's life. Comprehensive cancer care includes not only medical treatment but also psychological support, nutritional guidance, physical rehabilitation, and survivorship planning. Many cancer centers offer support groups, patient navigators, and integrative therapies to help patients manage the emotional and physical challenges of treatment and recovery.
After treatment completion, survivorship care includes regular follow-up visits, surveillance imaging, management of long-term treatment side effects, and screening for secondary cancers.