Breast Cancer: Complete Guide

Written by: Sarah Johnson, MD

Reviewed by: Oncol.net editorial team

Last reviewed: January 24, 2026

Quick Facts

Most common cancer in women worldwide
1 in 8 women will develop breast cancer in their lifetime
Early detection significantly improves outcomes
5-year relative survival rate for localized breast cancer is more than 99%
Multiple treatment options available based on type and stage

What is Breast Cancer?

Breast cancer is a disease in which cells in the breast grow out of control. It can begin in different parts of the breast, including the ducts, lobules, or tissue in between. While breast cancer occurs primarily in women, men can also develop this disease.

Key Points

Breast cancer is not a single disease but a group of diseases
Different types require different treatment approaches
Early detection through screening saves lives
Treatment is more effective when cancer is found early

The breast is made up of three main parts: lobules (glands that produce milk), ducts (tubes that carry milk to the nipple), and connective tissue. Most breast cancers begin in the ducts or lobules.

Types of Breast Cancer

Non-Invasive Types

Ductal Carcinoma In Situ (DCIS): Abnormal cells confined to milk ducts
Lobular Carcinoma In Situ (LCIS): Abnormal cells in lobules, considered a risk factor

Invasive Types

Invasive Ductal Carcinoma (IDC): Most common type (about 8 in 10 cases)
Invasive Lobular Carcinoma (ILC): Second most common (10-15% of cases)
Triple-Negative Breast Cancer: Lacks ER, PR, and HER2 receptors
HER2-Positive Breast Cancer: Overexpresses HER2 protein
Inflammatory Breast Cancer: Rare, aggressive form

Molecular Subtypes

Based on hormone receptor status and HER2 status:

Luminal A (ER+/PR+, HER2-, low Ki-67)
Luminal B (ER+/PR+, HER2+ or high Ki-67)
HER2-enriched (ER-, PR-, HER2+)
Basal-like (Triple negative)

Subtypes: HR-Positive, HER2-Positive, Triple-Negative

Two breast cancers can look alike under a microscope and still behave very differently. Doctors test the tumor for three markers: the estrogen receptor (ER), the progesterone receptor (PR), and the HER2 protein. These results set the subtype, and the subtype shapes treatment more than almost anything except stage.

All invasive breast cancers should be tested. The test is usually done on the biopsy sample, or on tissue removed during surgery. Your pathology report will list the results.

Subtype	What It Means	How Common	Main Drug Groups
Hormone receptor-positive (HR+)	Cells have ER, PR, or both. Hormones help them grow	About 3 in 4	Hormone therapy, often with targeted drugs
HER2-positive	Cells have too much HER2, a protein that drives growth	About 15-20%	HER2-targeted drugs with chemotherapy
Triple-negative	No ER, no PR, and not too much HER2	About 10-15%	Chemotherapy, immunotherapy, antibody-drug conjugates

These groups overlap. A cancer can be both HR-positive and HER2-positive, so the percentages do not add up to 100.

How HER2 Is Reported

The first test is often IHC, scored from 0 to 3+. A second test called FISH may follow.

HER2-positive: IHC 3+, or IHC 2+ with a positive FISH test
HER2-low: IHC 1+, or IHC 2+ with a negative FISH test. Some of these cancers may respond to antibody-drug conjugates
HER2-ultralow: IHC 0 with faint staining in up to 10% of cells
HER2-negative: IHC 0 with no staining of the cell membrane

Ask for a copy of your report, and ask which subtype applies to you.

Signs and Symptoms

Common Symptoms

New lump in breast or underarm
Thickening or swelling of part of the breast
Irritation or dimpling of breast skin
Redness or flaky skin in nipple area
Nipple discharge other than breast milk
Change in size or shape of breast
Pain in any area of the breast

⚠️ When to See a Doctor

Contact your healthcare provider immediately if you notice:

A new, hard lump or thickening in your breast
Bloody nipple discharge
Sudden breast skin changes
Inverted nipple (if new)

Causes and Risk Factors

Non-Modifiable Risk Factors

Age: Risk increases with age
Genetic mutations: BRCA1, BRCA2, and other genes. Up to about 10% of cases are thought to be hereditary. See our guide to BRCA testing
Family history: First-degree relatives with breast cancer
Personal history: Previous breast cancer or certain benign conditions
Dense breast tissue: Makes detection harder
Early menstruation: Before age 12
Late menopause: After age 55

Modifiable Risk Factors

Physical inactivity
Obesity after menopause
Hormone replacement therapy
Alcohol consumption
Reproductive history (no pregnancies or first pregnancy after 30)

Diagnosis

Screening Methods

Mammography: X-ray of the breast, gold standard for screening
Clinical breast exam: Physical examination by healthcare provider. The American Cancer Society does not recommend it for screening average-risk women
Breast self-exam: Optional, helps with breast awareness

Diagnostic Tests

Diagnostic mammography: Detailed X-ray
Breast ultrasound: Uses sound waves
Breast MRI: Detailed imaging using magnets
Biopsy: Tissue sample for definitive diagnosis
- Fine-needle aspiration
- Core needle biopsy
- Vacuum-assisted biopsy
- Surgical biopsy

Biomarker Testing

Tests performed on tumor tissue:

Estrogen receptor (ER) status
Progesterone receptor (PR) status
HER2 status
Ki-67 (proliferation marker)
Oncotype DX (21-gene test)

Staging

Breast cancer staging uses the TNM system and is grouped into stages 0-IV:

Stage	Description
Stage 0	DCIS - non-invasive, confined to ducts
Stage I	Small tumor (≤2cm), no lymph nodes or micrometastases
Stage II	Larger tumor and/or spread to few lymph nodes
Stage III	Locally advanced, multiple lymph nodes involved
Stage IV	Metastatic - spread to distant organs

Since 2018, the staging system has included ER, PR, and HER2 status, so a stage may be higher or lower than it would have been under the older system. Our breast cancer staging guide explains this in detail. US survival data are reported by how far the cancer has spread, not by stage number. See Prognosis and Survival Rates.

Treatment Options

Local Treatments

Surgery

Lumpectomy: Removes tumor and small margin of tissue
Mastectomy: Removes entire breast
Sentinel node biopsy: Checks first lymph nodes
Axillary dissection: Removes multiple lymph nodes

Radiation Therapy

External beam radiation
Brachytherapy (internal radiation)
Intraoperative radiation

Systemic Treatments

Chemotherapy

Common regimens include:

AC-T (Adriamycin, Cytoxan, Taxol)
TC (Taxotere, Cytoxan)
CMF (Cytoxan, Methotrexate, 5-FU)

Hormone Therapy

For ER/PR positive cancers:

Tamoxifen
Aromatase inhibitors (Letrozole, Anastrozole, Exemestane)
Fulvestrant, mainly for advanced cancer
Ovarian suppression

Targeted Therapy

For HER2-positive cancers:

Trastuzumab (Herceptin)
Pertuzumab (Perjeta)
T-DM1 (Kadcyla)
Tucatinib (Tukysa)

Immunotherapy

Pembrolizumab (Keytruda) for triple-negative

Treatment by Subtype

Most early breast cancers are treated with surgery, often with radiation. The subtype decides which drugs are added, and whether they are given before or after surgery. In stage IV, drugs are the main treatment. These cancers are very hard to cure, but many people live for years with treatment.

Hormone Receptor-Positive, HER2-Negative

Hormone therapy lowers estrogen or blocks it from reaching the cancer cells. After surgery, it is usually taken for at least 5 years, and common plans run 5 to 10 years.

After menopause: Usually an aromatase inhibitor such as letrozole, anastrozole, or exemestane. Tamoxifen is an option for those who cannot take one
Before menopause: Tamoxifen, with or without ovarian suppression, or an aromatase inhibitor with ovarian suppression. An aromatase inhibitor should not be used alone before menopause
Advanced cancer: Hormone therapy, including fulvestrant, is often combined with a CDK4/6 inhibitor such as palbociclib, ribociclib, or abemaciclib. PI3K inhibitors may be used for tumors with a PIK3CA mutation
Chemotherapy: Not everyone needs it. Your doctor will weigh stage, grade, and tumor tests such as Oncotype DX

HER2-Positive

HER2-targeted drugs attach to or block the HER2 protein. They are usually given with chemotherapy. If the cancer is also hormone receptor-positive, hormone therapy is often used as well.

Antibodies: Trastuzumab (Herceptin) and pertuzumab (Perjeta)
Antibody-drug conjugates: Trastuzumab emtansine (Kadcyla) and trastuzumab deruxtecan (Enhertu), which carry chemotherapy to the cancer cell
Pills: Tucatinib, neratinib, and lapatinib

Some HER2 drugs can affect the heart, so your team may check your heart function during treatment. Trastuzumab and doxorubicin are not given at the same time.

Triple-Negative

Hormone therapy and HER2 drugs do not work for these cancers. Chemotherapy has long been the main treatment, and newer options have been added.

Stages I-III: Pembrolizumab may be given with chemotherapy before surgery, and again afterward. If cancer remains after pre-surgery treatment, capecitabine may be used. People with a BRCA mutation may be offered olaparib for a year after chemotherapy
Stage IV, PD-L1 positive: Sacituzumab govitecan (Trodelvy) with pembrolizumab, or chemotherapy with pembrolizumab
Stage IV, PD-L1 negative: Sacituzumab govitecan, datopotamab deruxtecan (Datroway), or chemotherapy
BRCA or PALB2 mutation: Platinum drugs such as carboplatin, or PARP inhibitors such as olaparib or talazoparib

Should You Have BRCA Testing?

Inherited BRCA changes can affect drug choices, surgery decisions, and your relatives' screening. PARP inhibitors, for example, are used only for people with a BRCA mutation in some settings. Ask your doctor or a genetic counselor whether BRCA testing makes sense for you.

Prognosis and Survival Rates

Prognosis depends on multiple factors:

Stage at diagnosis
Tumor grade
Hormone receptor status
HER2 status
Patient age and overall health
Response to treatment

Overall Statistics

These are American Cancer Society figures for US women diagnosed from 2015 to 2021. Localized figures cover invasive cancer only, not DCIS.

5-year relative survival rate, all stages: 92%
Localized disease: more than 99% 5-year survival
Regional spread: 87% 5-year survival
Distant metastasis: 32% 5-year survival

Relative survival compares people with cancer to people in the general population. These figures describe large groups, not one person. They also reflect past treatment, so they may not capture recent advances.

Prevention

Risk Reduction Strategies

Maintain healthy weight
Exercise regularly (150 minutes/week)
Limit alcohol consumption
Avoid smoking
Breastfeed if possible
Limit hormone therapy

For High-Risk Individuals

Enhanced screening (MRI + mammography)
Chemoprevention (Tamoxifen, Raloxifene)
Prophylactic surgery (for BRCA carriers)
Genetic counseling and testing

Living with Breast Cancer

During Treatment

Managing side effects
Nutrition and exercise
Emotional support
Work and financial planning

After Treatment

Follow-up care schedule
Surveillance for recurrence
Managing long-term side effects
Healthy lifestyle maintenance

Frequently Asked Questions

Is breast cancer hereditary?

Up to about 10% of breast cancers are thought to be hereditary, caused by inherited gene mutations like BRCA1 and BRCA2. Having a family history increases risk but doesn't guarantee developing cancer.

Can men get breast cancer?

Yes, though rare. Fewer than 1% of breast cancers occur in men. Risk factors include BRCA2 mutations, Klinefelter syndrome, and family history.

What age should screening start?

Guidelines vary. The US Preventive Services Task Force recommends a mammogram every 2 years from age 40 to 74. The American Cancer Society says yearly mammograms are optional from 40 to 44 and recommended from 45 to 54. High-risk individuals may start earlier with additional screening methods.

Does breast cancer always require chemotherapy?

No. Treatment depends on cancer type, stage, and molecular features. Some early-stage, hormone-positive cancers may be treated with surgery and hormone therapy alone.

What is the difference between DCIS and invasive breast cancer?

DCIS (Stage 0) is confined to milk ducts and hasn't spread. Invasive cancer has spread beyond ducts into surrounding breast tissue and potentially beyond.

What are the main subtypes of breast cancer?

Doctors group invasive breast cancers by testing for hormone receptors and HER2. The main groups are hormone receptor-positive, HER2-positive, and triple-negative. A cancer can be both hormone receptor-positive and HER2-positive. The subtype helps decide which drugs are likely to work.

What does triple-negative breast cancer mean?

It means the cancer cells test negative for estrogen receptors and progesterone receptors and do not have too much HER2. Hormone therapy and HER2-targeted drugs do not help these cancers, so treatment usually relies on chemotherapy, immunotherapy, and other targeted drugs. It makes up about 10% to 15% of breast cancers.

How long does hormone therapy last?

After surgery, it is usually taken for at least 5 years. Common plans run 5 to 10 years. People at higher risk of the cancer coming back may be offered the longer course.

Who should have BRCA testing?

Talk with your doctor or a genetic counselor if you have a strong family history of breast or ovarian cancer, or if you have been diagnosed with breast cancer, especially at a young age or with triple-negative disease. A BRCA result can guide both treatment and screening for relatives.

Sources

National Cancer Institute. Breast Cancer Treatment (PDQ) - Health Professional Version. Updated January 2026.
American Cancer Society. Breast Cancer Facts & Figures 2025-2026.
NCCN Guidelines. Breast Cancer. Version 1.2026.
Siegel RL, et al. Cancer Statistics, 2026. CA Cancer J Clin. 2026.
ASCO Clinical Practice Guidelines. Breast Cancer. 2025.
Breast Cancer Hormone Receptor Status, American Cancer Society
Breast Cancer HER2 Status, American Cancer Society
Triple-negative Breast Cancer, American Cancer Society
Hormone Therapy for Breast Cancer, American Cancer Society
Targeted Drug Therapy for Breast Cancer, American Cancer Society
Treatment of Triple-negative Breast Cancer, American Cancer Society
Immunotherapy for Breast Cancer, American Cancer Society
Treatment of Breast Cancer by Stage, American Cancer Society
Hormone Therapy for Breast Cancer, National Cancer Institute
Survival Rates for Breast Cancer, American Cancer Society
Cancer Stat Facts: Female Breast Cancer, SEER, National Cancer Institute
Key Statistics for Breast Cancer, American Cancer Society
Key Statistics for Breast Cancer in Men, American Cancer Society
Breast Cancer Risk Factors You Cannot Change, American Cancer Society
Breast Cancer: Screening, US Preventive Services Task Force
American Cancer Society Recommendations for the Early Detection of Breast Cancer