How Does Treatment Differ by Breast Cancer Subtype? (2026 Update)

Breast cancer is a disease where the order of surgery and the drugs used can vary greatly depending on the subtype, which is determined by hormone receptor (ER·PR), HER2, and Ki-67 test results. Even at the same stage, a different subtype means a completely different treatment path.

Key Takeaways

• Breast cancer isn't a single disease — it's grouped into subtypes based on ER, PR, HER2, and Ki-67 results, and these subtypes show different courses and treatments.
• Korea's 5-year relative survival rate for breast cancer is 94.7% (National Cancer Registry Statistics 2019–2023, National Cancer Center Korea's Central Cancer Registry), but this is a nationwide figure and does not predict any individual's outcome.
• For HER2-positive or triple-negative breast cancer, especially at stage 3, the standard approach is often to start with chemotherapy (combined with targeted therapy for HER2-positive disease) before surgery.
• If hormone receptors are positive, oral hormone therapy continues for 5 to 10 years after surgery, and at stage 4, combining this with a CDK4/6 inhibitor is a common regimen.
• A biopsy needs to check all four markers together — ER, PR, HER2, and Ki-67 — to build a treatment plan.

How Is the Subtype Determined?

• If a lump is felt in the breast or an abnormality shows up on screening, mammography and ultrasound are performed first, and the diagnosis is confirmed with a needle biopsy of the suspicious area.
• This biopsy checks not only whether cancer is present and its tissue type, but also the estrogen receptor (ER), progesterone receptor (PR), HER2 status, and Ki-67 (which reflects how fast the cells are dividing). These four results form the starting point for the treatment plan.
• To determine the stage, breast MRI and axillary ultrasound are done, and if needed, chest CT, abdominal imaging, bone scan, or PET-CT are added to check for distant metastasis. For younger patients or those with a family history, BRCA1/2 genetic testing may be used, and for early-stage hormone receptor-positive cancer, a multigene test may be used to decide whether chemotherapy is needed.

How Does Treatment Order Change by Subtype?

• For stage 1–2 disease, surgery is the main approach. If the tumor-to-breast size ratio allows, breast-conserving surgery is followed by radiation therapy, and after surgery, chemotherapy, anti-HER2 targeted therapy, hormone therapy, and radiation therapy are combined depending on the subtype and stage.
• For stage 3 disease, or HER2-positive or triple-negative cancer, the standard is to give chemotherapy first (plus targeted therapy if HER2-positive) before surgery, to shrink the tumor and directly see whether the drugs are working. This increases the chance of breast-conserving surgery, and the drugs used afterward are chosen based on how much tumor remains after surgery.
• For stage 4 (metastatic) disease, the goal shifts from cure to maintaining comfort and control over the long term. If hormone receptor-positive, a CDK4/6 inhibitor is added to hormone therapy; if HER2-positive, anti-HER2 targeted therapy and antibody-drug conjugates are used; if triple-negative, chemotherapy is combined with immunotherapy or antibody-drug conjugates — the options differ by subtype.
• For hormone receptor-positive disease, oral hormone therapy continues for 5 to 10 years after surgery. The specific drug differs depending on whether the patient is pre- or post-menopausal, and an ovarian function suppression injection may be added in some cases.

Does the Surgical Approach Also Differ by Subtype?

• Step 1: If the tumor-to-breast size ratio and location allow, breast-conserving surgery and oncoplastic techniques are considered.
• Step 2: If the tumor is large or scattered across multiple areas, total mastectomy is performed, and immediate reconstruction using implants or autologous tissue can be done in the same surgery. If radiation therapy is planned, the timing and method of reconstruction are adjusted accordingly.
• Step 3: For the axilla, a sentinel lymph node biopsy is done first to check for spread. If there's no or minimal spread, extensive lymph node removal is avoided, reducing the risk of arm lymphedema.
• Step 4: After treatment ends, follow-up exams and mammograms are repeated at set intervals. For patients on hormone therapy, bone density and gynecologic exams are also checked, and for those on anti-HER2 therapy, heart function is monitored.

FAQ — What if the subtype test results are borderline?

HER2 results can vary depending on the testing method and scoring criteria, and since this result determines which drugs are used, retesting with the paraffin block is sometimes recommended when the score is borderline. Test results obtained overseas can generally still be used as reference material.

FAQ — Are survival rates broken down by subtype?

The published overall 5-year relative survival rate for breast cancer is 94.7% (National Cancer Registry Statistics 2019–2023), but this is a nationwide figure, and actual outcomes vary significantly by subtype and stage. Your own subtype and stage matter more than the overall number when gauging your likely course.

Sources and Notes

• This article was written based on the National Cancer Registry Statistics 2019–2023 (National Cancer Center Korea's Central Cancer Registry), NCCN patient guidelines, and SEER statistics.
• This content is intended for general medical information purposes only. Diagnosis, treatment methods, and outcomes may vary depending on individual condition. Please consult with your medical team to determine an accurate diagnosis and treatment plan.