Cancer - breast
Description
Histology
- Invasive ductal (NST) 75-80%
- Invasive lobular 10-15% - arises from terminal duct lobular unit
- Lower grade, E-cadherin negative, diffuse infiltration
- Poorly seen on mammography; bilateral + multifocal more often; metastasises to peritoneum, GIT, ovary
- Special types: tubular, mucinous, medullary (better prognosis)
In situ
- DCIS - true precursor, treat as cancer (excision +/- RT +/- endocrine)
- LCIS - a risk marker, not a precursor; risk to both breasts
Molecular subtypes - the axis that drives everything
| Subtype | Receptors | Proliferation | Systemic therapy |
|---|---|---|---|
| Luminal A | ER/PR+++, HER2- | Low (Ki67 low) | Endocrine alone |
| Luminal B | ER/PR+, HER2- | High | Chemo + endocrine |
| HER2-positive | HER2 amplified | High | Chemo + anti-HER2 (+ endocrine if ER+) |
| Basal / TNBC | ER-, PR-, HER2- | High | Chemo (+ immunotherapy, PARPi) |
- HER2-low / HER2-ultralow now a distinct therapeutic category (IHC 1+ or 2+/ISH-, and faint incomplete staining)
- Not a biological subtype - a predictive category for trastuzumab deruxtecan
Special presentations
- Inflammatory - peau d'orange, erythema, no discrete lump; dermal lymphatic invasion; stage III minimum, poor prognosis
- Paget's of nipple - eczematous nipple, underlying DCIS/invasive in most
- Occult primary - axillary node adenocarcinoma, normal imaging -> breast MRI
6 more sections, plus exam facts
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