Categories of Breast Cancer

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1. Major Categories of Breast Cancer

Breast cancer is not a single disease. It’s classified by where it starts, how aggressive it is, what markers (receptors) it has, and whether it has spread.

A. Non-Invasive (“in situ”)

• Ductal Carcinoma In Situ (DCIS): Occurs in the milk ducts, hasn’t invaded surrounding tissue. Cancer.org+1

• Lobular Carcinoma In Situ (LCIS): Abnormal cells in the lobules (milk-producing glands), but not invasive. It’s sometimes considered a risk marker. Breast Cancer Research Foundation+1

These are sometimes called stage 0 cancers (or pre-cancers) because they haven’t broken out. Cancer.org+1

B. Invasive (or “infiltrating”)

These cancers have broken out of where they started and invaded surrounding tissue. Breast Cancer Research Foundation+2BreastCancer.org+2

Common subtypes:

Type	Origin / Definition	Notes
Invasive Ductal Carcinoma (IDC)	Starts in the milk ducts, then invades outwards	The most common type (~70-80% of breast cancers) Breast Cancer Research Foundation+2Cancer.org+2
Invasive Lobular Carcinoma (ILC)	Starts in the lobules, then invades	Has a different growth pattern — sometimes more diffuse in breast tissue Breast Cancer Research Foundation+2BreastCancer.org+2

Less common / special types:

• Inflammatory Breast Cancer (IBC): aggressive, often without a distinct lump. Presents with redness, swelling, “peau d’orange” skin texture. National Cancer Institute+2Breast Cancer Research Foundation+2

• Triple-Negative Breast Cancer (TNBC): Lacks estrogen receptor (ER), progesterone receptor (PR), and HER2 protein. More aggressive. Cancer.org+4National Cancer Institute+4Breast Cancer Research Foundation+4

• HER2+ breast cancer: Overexpresses the HER2 protein (a growth factor receptor) — can be more aggressive but has targeted therapies. Cancer.org+3National Cancer Institute+3Breast Cancer Research Foundation+3

• Other rare types: e.g. Paget’s disease of the nipple, metaplastic carcinoma, angiosarcoma, etc. Breast Cancer Research Foundation+2BreastCancer.org+2

Additionally, cancers are classified by molecular subtype / receptor status (hormone receptor positive/negative, HER2 positive/negative) — these influence treatment and prognosis

2. Key Factors That Change Treatment Strategy

When deciding how to treat a breast cancer, doctors look at:

• Stage / extent — how big the tumor, whether it has spread to lymph nodes or distant organs. National Cancer Institute+2Cancer.org+2

• Grade — how abnormal the cancer cells look under microscope (low grade = more like normal cells)

• Receptor / biomarker status — whether cancer cells have estrogen receptors (ER+), progesterone receptors (PR+), HER2 overexpression, etc. Breast Cancer Research Foundation+3National Cancer Institute+3Susan G. Komen®+3

• Patient health, preferences — age, other medical conditions, choice, etc.

3. Treatments (by Type / Stage / Subtype)

Treatments fall into local (targeting where the cancer is) vs systemic (drugs that go through the body). Mayo Clinic+4Cancer.org+4National Cancer Institute+4

Local Therapies

• Surgery

  • Lumpectomy / breast-conserving surgery (remove tumor + some margin)

  • Mastectomy (remove entire breast)

  • Sometimes remove lymph nodes or do sentinel node biopsy

  • Surgery may come first or sometimes after (neoadjuvant) therapy to shrink tumor. National Breast Cancer Foundation+3Mayo Clinic+3National Cancer Institute+3

• Radiation therapy

• After surgery (especially for lumpectomy) to kill residual cancer cells

• Sometimes used before surgery or for palliation (symptom control

Systemic Therapies (Drug / Whole-Body)

These are especially important when there’s risk of cancer spreading or in advanced stages.

• Chemotherapy
  Uses anti-cancer drugs that travel via bloodstream to kill or stop cancer cells.
  Often part of treatment for more aggressive or higher-stage disease. National Breast Cancer Foundation+3Mayo Clinic Cancer Blog+3National Cancer Institute+3

• Hormone (Endocrine) Therapy
  For cancers that are hormone receptor positive (ER+, PR+)
  Blocks or lowers estrogen (or blocks receptors) so cancer cells can't use it to grow.
  Drugs include tamoxifen, aromatase inhibitors, etc. Mayo Clinic Cancer Blog+3National Cancer Institute+3Susan G. Komen®+3

• Targeted Therapy
  Drugs that target specific features (biomarkers) of cancer cells
  E.g. HER2-targeted therapy (trastuzumab / Herceptin, pertuzumab) for HER2+ cancers. National Breast Cancer Foundation+3Cancer.org+3National Cancer Institute+3
  Also newer drugs (e.g. for cancers with certain mutations) National Cancer Institute+2Mayo Clinic Cancer Blog+2

• Immunotherapy / Biological / Checkpoint Inhibitors
  Treatments that help the immune system attack cancer.
  Used in select cases (e.g. some triple-negative cancers) Mayo Clinic Cancer Blog+2National Cancer Institute+2

• Other / Emerging therapies
  E.g. PARP inhibitors (for BRCA mutation cancers), CDK 4/6 inhibitors (in hormone receptor positive cancers), etc.

• 4. How Treatment Varies by Type / Stage

  Here are some examples of how subtype / stage affects what treatments are chosen:

  • DCIS (non-invasive)
    Often treated with surgery + radiation. Sometimes hormone therapy if hormone receptor positive. Canadian Cancer Society+2BreastCancer.org+2

  • Early (localized) invasive cancers (Stage I, II, III)
    Usually surgery + radiation + systemic therapy (chemo, hormone, targeted) depending on risk & subtype. Cancer Research UK+3Cancer.org+3National Cancer Institute+3

  • HER2+ cancers
    In addition to standard surgery / radiation / chemo, they also get HER2-targeted therapy (to fight the HER2 protein).

  • Hormone receptor positive (ER+/PR+) cancers
    Likely receive hormone therapy (sometimes for many years) to reduce recurrence risk.

  • Triple-negative cancers
    Because they lack receptors, hormone or HER2 therapies don’t work. The main systemic therapy is chemotherapy; immunotherapy in selected cases.

  • Metastatic (Stage IV / spread to distant sites)
    Focus is on systemic therapy (targeted, hormone, chemo, immunotherapy) to control disease, prolong life, manage symptoms. Surgery/radiation may be used for symptom control.

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