• Clinical science

Breast cancer


Breast cancer is the most common malignancy in women. The lifetime risk of developing breast cancer for women in the USA is approx. 12%. The most important risk factors include increased estrogen exposure, advanced age, and genetic predisposition (BRCA1/BRCA2 mutations). Most breast cancers are adenocarcinomas. Histopathologic classification differentiates between ductal and lobular carcinomas. The two most common types of breast cancer are invasive ductal carcinoma, which accounts for 70–80% of all cases, and the less aggressive invasive lobular carcinoma. Both types typically develop from noninvasive carcinomas, i.e., ductal carcinoma in situ (DCIS), and lobular carcinoma in situ (LCIS), respectively.

The majority of breast cancers are detected during routine mammography screening, which is recommended every two years in women aged 50–74 years. Alternatively, women may present with a self-palpated breast lump. Mammographic abnormalities and breast masses require further radiographic evaluation, and, if there are signs of malignancy or the results are inconclusive, histopathologic analysis (biopsy). The axillary lymph node status is determined through clinical examination and biopsy of a suspicious lymph node or sentinel lymph node.

The treatment approach primarily depends on the histopathologic classification and the disease stage and involves a combination of surgical management, radiation therapy, and systemic therapy. Surgical management is either breast-conserving therapy (BCT) or mastectomy. Systemic therapy has significantly improved in recent years with the development of hormone therapy (tamoxifen) and targeted therapy (trastuzumab). The most important prognostic factors are lymph node status, tumor size, patient's age, and tumor receptor status (hormone receptors and HER2).

Women with a high risk of developing breast cancer (i.e., positive BRCA mutation status) should be offered genetic counseling and risk-reducing prophylactic surgery.


One in 8 women in the USA (∼12 %) will develop invasive breast cancer during their lifetime!


Epidemiological data refers to the US, unless otherwise specified.


Predisposing factors

Associated genetic diseases



Most breast cancers are adenocarcinomas, arising from ductal tissue (80%) or lobular tissue (20%).

Noninvasive (in situ) carcinomas

The noninvasive carcinomas are characterized by the absence of stromal invasion!

Invasive carcinomas


Clinical features

Patients with breast cancer develop clinical symptoms rather late at advanced tumor stages. Typical signs may include:

  • Changes in breast size and/or shape; asymmetric breasts
  • Palpable mass: typically a single, nontender, firm mass with poorly defined margins; , most commonly in the upper outer quadrant
  • Skin changes
    • Retractions or dimpling (due to tightening of the Cooper ligaments)
    • Peau d'orange: skin resembling an orange peel (due to obstruction of the lymphatic channels)
  • Nipple changes: inversion, blood-tinged discharge
  • Axillary lymphadenopathy: firm, enlarged lymph nodes (> 1 cm in size), that are fixed to the skin or surrounding tissue
  • In advanced stages: ulcerations


Subtypes and variants

Paget disease of the breast

Inflammatory breast cancer



Approach to suspected breast cancer

Most patients present with abnormalities detected during routine mammography screening. Alternatively, young women in particular (who are not routinely screened) present with a self-palpated breast mass. The diagnostic approach involves clinical assessment, radiographic imaging, and biopsy.

Clinical scenario First step
  • Women < 30 years with a self-palpated breast lump
  • Women > 30 years with self-palpated breast lump or mammographic abnormalities detected during breast cancer screening

Clinical assessment

Certain constellations of patient characteristics should raise suspicion for malignancy in a breast lump, warranting further assessment.

Nonsuspicious Suspicious
  • Age < 35 years
  • No family history
  • Soft, movable mass
  • Size changes with menstruation cycle

Radiographic imaging


Although mammography does not confirm the diagnosis, it is primarily useful for early detection of breast abnormalities!

Benign Malignant
  • Well-defined, circumscribed mass
  • Radiolucent ring surrounding the lesion (halo sign)
  • Diffuse microcalcification or coarse calcification
  • Focal mass or density with poorly defined margins
  • Spiculated margins
  • Clustered microcalcifications

Breast ultrasound

  • Distinguish between solid lesions and benign cysts
  • Evaluate axillary, supraclavicular, and infraclavicular lymph nodes
  • Provide guidance in interventional procedures (fine needle aspiration, core needle biopsy)


Core needle biopsy (CNB) : confirms the diagnosis (preferred test) and can distinguish between noninvasive and invasive carcinoma based on histology; indicated for a suspicious breast mass on ultrasound or mammography.

Workup of diagnosed breast cancer

Axillary lymph node involvement suggests that hematogenic spread has already occurred!



Noninvasive carcinomas

Type Characteristics Growth pattern
  • Macroscopic: firm mass may be visible
  • Microscopic
    • Enlarged ducts lined with atypical epithelium
    • Intact basal membrane
    • Microcalcifications are noted occasionally.
  • Macroscopic: not visible
  • Microscopic
    • The lobules are filled with monomorphic cells.
    • Intact basal membrane
  • Diffuse

Invasive carcinomas

Type Characteristics Growth pattern
Invasive ductal
  • Macroscopic: firm tumor, fibrous, grayish-white cut surface
  • Microscopic: disorganized, small duct-like glandular cells with stromal invasion, microcalcifications, and fibrosis in surrounding tissue
  • Unilateral
Invasive lobular
  • Macroscopic: solid
  • Microscopic
    • Malignant cells in lobules
    • Monomorphic cells in a single file pattern ("Indian file" pattern
  • Unilateral or bilateral
  • Well circumscribed tumor
  • Poorly differentiated cells with syncytial growth with lymphocytic infiltrates
  • Rapid growth
  • Well circumscribed tumor
  • Extracellular mucus
  • Slow growth
  • Well-differentiated tubular structures, stromal invasion (radial pattern)
  • Slow growth
  • Dermal lymphatic invasion, angioinvasion
  • Rapid growth


Differential diagnoses

Breast mass Nipple discharge Skin changes Ultrasound/Mammography Biopsy
Benign Nonneoplastic Fibrocystic breast changes
  • Clear or slightly milky
  • None
  • Normal appearance or focal regions of thick parenchyma
  • Clear borders
  • +/- cysts
  • +/- dispersed calcifications
  • Stromal fibrosis
  • Cysts
  • Papillary apocrine changes
  • Mild epithelial hyperplasiaorcalcifications
  • Firm, concentric, sometimes tender mass at the nipple areolar complex
  • None
  • None
  • Mammogram only required in doubtful or persistent cases)
  • Unnecessary
Inflammatory Mastitis
  • Milky
  • Bloody
  • Unnecessary
  • Unnecessary
  • Milk sampling + culture only if initial treatment fails
Fat necrosis
  • Irregularly defined and dense periareolar breast mass
  • Fluid-filled cyst
  • Course rim calcification
Breast abscess
  • Fluctuant mass
Eczema of the breast
  • None
  • None
  • Eczematous rash with poorly defined margins and no infiltration
  • Unnecessary
  • Only if diagnosis is inconclusive or malignancy is suspected
Neoplastic Fibroadenoma
  • Solitary, well-defined, non-tender, rubbery and mobile mass
  • Well-defined mass
  • Possibly popcorn-like calcifications
Phyllodes tumor
  • Painless, smooth, multinodular lump
  • Variable growth rate
  • Generally > 3 cm
Intraductal papilloma
  • Solitary lesions: palpable breast tumor close to or behind the nipple
  • Multiple lesions: usually asymptomatic
  • Bloody (most common cause)
  • None
Malignant Invasive carcinoma (ductal and lobular)
  • Bloody
  • Focal mass or density with poorly defined margins
  • Spiculated margins
  • Clustered microcalcifications
  • Ductal: malignant cells in duct, stromal invasion, microcalcifications, fibrosis in surrounding tissue
  • Lobular: malignant cells in lobules; monomorphic cells in a single file pattern ("Indian file" pattern)
Inflammatory breast cancer
  • Blood-tinged
  • Dermal lymphatic invasion, angioinvasion
Paget disease of the breast
  • Blood-tinged (when the lesion ulcerates)
Other rare breast malignancies


The differential diagnoses listed here are not exhaustive.


The treatment approach primarily depends on the histopathologic classification and disease stage and involves a combination of surgical management and systemic therapy (chemotherapy, hormone therapy, targeted therapy). Patient preference for more or less aggressive management also plays a significant role in selecting the treatment approach.

Invasive carcinoma

  • Early stage disease
    • Breast-conserving therapy (BCT): lumpectomy followed by radiation therapy
      • Contraindications: large tumor-to-breast ratio, multifocal tumors, fixation to the chest wall, excision with negative tumor margins (> 2 mm) not guaranteed, clustered microcalcifications on imaging, involvement of the skin or nipple, a history of chest radiation
      • Surgical margins need to be tumor free . Otherwise, repeat resection or consider mastectomy.
      • Consider mastectomy for anyone unable to undergo BCT or who requests a more aggressive management.
    • Intraoperative lymph node evaluation
    • Adjuvant systemic therapy
      • Hormone and targeted biologic therapy in all ER/PR+ or HER2+ patients
      • Chemotherapy in high-risk patients (see table under "Systemic therapy” below)
  • Locally advanced disease
    • Neoadjuvant systemic therapy + surgical resection (BCT or mastectomy) + axillary lymph node dissection
    • Followed by adjuvant systemic therapy ± radiation therapy
  • Advanced metastatic disease: systemic treatment followed by palliative surgery and/or radiation therapy
  • Gestational breast cancer

Noninvasive carcinoma

Systemic therapy

Indications Agents Side effects and contraindications
Hormone therapy
  • ER or PR positive tumors
Targeted therapy
  • HER2-positive tumors

Tamoxifen acts as an agonist on endometrial estrogen receptors, thereby increasing the risk of endometrial cancer.



Relapse typically occurs within the first five years after completion of treatment!


We list the most important complications. The selection is not exhaustive.


Prognostic factors

  • Axillary lymph node status (most important prognostic factor)
  • Tumor size
  • Patient's age
  • Receptor status (ER/PR-negative and triple-negative disease are associated with a worse prognosis)
    • Histologic grade and subtype

HER2-positive cancers demonstrate a more aggressive tumor growth and higher recurrence rates and therefore are associated with a poor prognosis. Since the development of targeted therapy with trastuzumab, the prognosis for patients with HER2-positive cancers has improved!


  • Early-stage disease without lymph node involvement
    • 10-year survival rate: 70%
  • Node-positive disease: high risk of recurrence
  • Metastatic disease: 3-year survival rate of 48–71%



Breast cancer screening

  • Mammography: every 2 years in average-risk women aged 50–74 years
    • Two views of the breast are obtained: mediolateral oblique and craniocaudal
  • Physical examination plays a minor role in screening for breast cancer.

If the cancerous lesion is detectable by palpation, a stage II tumor or higher (size > 2 cm) is very likely!
Mammography has greatly improved early detection of noninvasive carcinomas! While DCIS can occasionally be detected as a palpable lump, LCIS cannot be detected by clinical examination.

Prevention in high-risk women



Early stage disease
  • Localized tumor (< 5 cm)
  • ≤ 3 nodes involved, including the sentinel lymph node
Locally advanced disease
Advanced metastatic disease