PA30.1-5 | Breast — Glossary

Bacterial infection of the breast, predominantly by Staphylococcus aureus, occurring during lactation; may progress to abscess formation

Replacement of normal ductal epithelium by cells with abundant eosinophilic granular cytoplasm and prominent nucleoli, resembling apocrine sweat glands; a benign finding in fibrocystic change

Enzyme (CYP19A1) that converts androgens (androstenedione, testosterone) to estrogens (estrone, estradiol); expressed in adipose tissue, liver, skin, and brain; activity is increased in obesity, liver disease, and aging

Proliferation of ductal epithelial cells with cytological and architectural features resembling low-grade DCIS but quantitatively less (partial duct involvement); associated with 4–5× increased carcinoma risk

Partial filling of lobular acini by small, monomorphic cells resembling those of lobular carcinoma in situ; associated with 4–5× increased carcinoma risk (bilateral)

Extracellular matrix separating epithelium from stroma; intact in benign and in-situ lesions; breached in invasive carcinoma.

A macroscopic breast cyst in fibrocystic change with a translucent blue-green wall, produced by tension and the visible blood vessels through the thin cyst wall; lined by flattened or apocrine epithelium

Tumour suppressor gene on chromosome 17q21 encoding a DNA damage repair protein; germline mutations confer 50–80% lifetime breast cancer risk; associated predominantly with triple-negative/basal-like carcinoma.

Tumour suppressor gene on chromosome 13q12–13 encoding a homologous recombination repair protein; germline mutations give 40–70% lifetime risk; associated with ER-positive carcinoma and male breast cancer.

High-grade DCIS pattern with central coagulative necrosis that undergoes calcification, producing linear/branching microcalcifications on mammography; high risk of progression to invasive carcinoma.

Central necrosis within ducts in high-grade DCIS, expressed as toothpaste-like material from cut duct cross-sections; calcifies to form branching microcalcifications on mammography.

Malignant proliferation of ductal epithelial cells confined within the basement membrane, with no stromal invasion; classified by architecture (comedo, cribriform, micropapillary, papillary, solid) and nuclear grade.

Dense fibrous stroma produced by reactive fibroblasts in response to tumour invasion; responsible for the firm, gritty texture of invasive ductal carcinoma NST on gross examination.

Dilatation of major subareolar ducts with inspissated secretions; a precursor change in periductal mastitis; may cause nipple discharge and subareolar mass

Stepwise progression from normal ductal epithelium → usual ductal hyperplasia → atypical ductal hyperplasia → DCIS → invasive ductal carcinoma; accumulates mutations in ER, HER2, TP53, and CDKN2A over 10–15 years.

Cell-cell adhesion transmembrane glycoprotein encoded by CDH1 (16q); loss of expression causes cell discohesion; absent in lobular neoplasia (LCIS and ILC), present in ductal lesions.

Reactive necrosis of adipose tissue following trauma or ischemia, characterised by ghost adipocytes, lipophage macrophages, and dystrophic calcification; clinically and radiologically simulates carcinoma

The most common benign breast tumor, arising from intralobular stroma, comprising a biphasic proliferation of stroma and ducts; estrogen-sensitive, most common in women aged 15–35 years

A spectrum of histological alterations in the breast (cysts, apocrine metaplasia, fibrosis, epithelial hyperplasia) representing exaggerated or aberrant responses to cyclic hormonal stimulation; not a single disease entity

Late, inactive phase of gynecomastia characterised by dense hyalinised periductal fibrosis with few residual ducts; irreversible even after removal of the causative stimulus

Molecular cytogenetic technique using fluorescent DNA probes to detect gene copy number; used to assess HER2 gene amplification when IHC score is 2+ (equivocal); HER2/CEP17 ratio >2.0 = amplified = positive.

Early, active phase of gynecomastia characterised by ductal hyperplasia and loose edematous periductal stroma; potentially reversible if the causative stimulus is removed

Anucleate adipocyte outlines with eosinophilic granular cytoplasm seen in fat necrosis, representing necrotic adipocytes whose nuclei have dissolved

Benign glandular proliferation of the male breast driven by an altered estrogen/androgen ratio; characterised histologically by ductal epithelial hyperplasia and periductal stromal proliferation with absence of lobules

Spread of tumor cells via blood vessels; the route taken by phyllodes tumor (to lung) and distinct from the lymphatic route of most breast carcinomas.

Human epidermal growth factor receptor 2; receptor tyrosine kinase encoded on chromosome 17q12; amplification (~15–20% of breast carcinomas) drives tumour proliferation and predicts response to trastuzumab.

Sarcomatous differentiation within phyllodes tumor stroma (liposarcoma, rhabdomyosarcoma, chondrosarcoma, osteosarcoma); their presence defines malignant grade.

High-fidelity DNA repair pathway that uses the sister chromatid as a template to repair double-strand breaks; requires functional BRCA1/2 proteins; defective in hereditary breast/ovarian cancer syndrome.

Characteristic growth pattern of invasive lobular carcinoma in which discohesive tumor cells infiltrate in single-file linear cords through fibrous stroma.

Clinical-pathological diagnosis: rapid-onset diffuse breast erythema, warmth and oedema (peau d'orange) with histological demonstration of tumour cell emboli in dermal lymphatics; classified T4d; requires neoadjuvant chemotherapy.

Growth pattern of fibroadenoma in which proliferating stroma compresses duct spaces into curved slit-like ('antler-horn') configurations

A benign epithelial tumor forming branching fibrovascular papillary fronds within a dilated duct, lined by both luminal and myoepithelial cells; the commonest cause of bloody nipple discharge

Most common invasive breast carcinoma (50–70%); no special type architecture; characterized by desmoplasia and infiltrating nests of pleomorphic cells.

Most common invasive breast carcinoma (~70–80%); firm stellate tumour with desmoplastic stroma; lacks sufficient features to classify as a special type.

Second most common invasive breast carcinoma; characterised by single-file (Indian file) arrangement, E-cadherin loss, minimal desmoplasia, and ER+ phenotype; may metastasise to peritoneum and GI tract.

Nuclear protein expressed in proliferating cells; IHC percentage of Ki-67-positive nuclei = proliferation index; cutoff ~14–20%; high Ki-67 correlates with aggressive subtype (Luminal B, HER2-enriched, TNBC).

Chromosomal condition (47,XXY) causing primary hypogonadism, reduced testosterone, and relative estrogen excess; the condition most strongly associated with male breast carcinoma (20–50× increased risk)

Neoplastic proliferation filling and distending the terminal duct-lobular unit without invasion; characterised by loss of E-cadherin; acts as a bilateral risk marker rather than a direct precursor.

A lipid-laden macrophage (foamy macrophage) that engulfs fat released from necrotic adipocytes; a characteristic feature of fat necrosis

Molecular subtype: ER+/PR+/HER2−/Ki-67 low (<20%); best prognosis; treated with endocrine therapy alone; histologically usually Grade 1–2.

Tumour cells within lymphatic channels or blood vessels in the breast parenchyma adjacent to the primary tumour; independent prognostic factor predicting axillary nodal involvement and distant metastasis.

Special-type invasive carcinoma: syncytial growth pattern, high-grade nuclei, prominent lymphoplasmacytic stroma, well-circumscribed margins, triple-negative phenotype; paradoxically better prognosis due to immune infiltrate; linked to BRCA1.

Special-type invasive carcinoma of older women: small uniform low-grade cells floating in abundant extracellular mucin pools; ER-positive; excellent prognosis (>90% 10-year survival for pure mucinous).

Contractile cell lining the outer aspect of breast ducts and acini, between luminal epithelium and basement membrane; acts as the sentinel of benignity — its absence suggests malignancy

Histological grading for invasive breast carcinoma scoring tubule formation, nuclear pleomorphism, and mitotic count (each 1–3); total 3–5 = Grade 1, 6–7 = Grade 2, 8–9 = Grade 3.

Three-component grading system for invasive breast carcinoma (Bloom-Richardson-Elston): tubule formation + nuclear pleomorphism + mitotic count, each scored 1–3; total 3–5 = Grade 1, 6–7 = Grade 2, 8–9 = Grade 3.

Nuclear transcription factor expressed by myoepithelial cells; used as an immunohistochemical marker to confirm presence of myoepithelial layer in distinguishing benign from malignant breast lesions

Large, pale, vacuolated malignant cells (Paget cells) within the squamous epidermis of the nipple-areola complex, arising from upward migration of underlying DCIS or invasive carcinoma cells.

Class of targeted agents (e.g. olaparib, niraparib) that block poly-ADP-ribose polymerase, a DNA repair enzyme; BRCA1/2-mutant tumours cannot repair the resulting double-strand breaks → synthetic lethality; used in BRCA-mutant TNBC.

Orange-peel skin texture of the breast caused by dermal lymphoedema due to tumour obstruction of lymphatic channels, tethering the skin at sweat-gland apertures; hallmark of inflammatory carcinoma.

Growth pattern of fibroadenoma in which stroma proliferates around ducts that remain open and round

Inflammatory condition of non-lactating breast caused by duct ectasia and leakage of lipid-rich secretions; characterised by periductal plasma cell infiltration, fibrosis, and nipple discharge; can mimic carcinoma

A fibroepithelial breast tumor characterised by hypercellular, mitotically active stroma with leaf-like intracanalicular projections; classified as benign, borderline, or malignant based on stromal features

Breast enlargement in males due to adipose deposition without true glandular proliferation; distinguished from gynecomastia by the absence of a firm retroareolar disc on palpation and absence of ductal hyperplasia on histology

Lobulocentric proliferation of acini and myoepithelial cells within fibrous stroma; mimics carcinoma histologically but retains lobular architecture and myoepithelial cells; benign

Removal and histological examination of the first draining (sentinel) axillary lymph node, identified by blue dye or radiocolloid injection; if negative, full axillary dissection is avoided, reducing morbidity.

Complete replacement of the epithelial component by stroma in at least one ×4 (low-power) field; the WHO parameter most strongly associated with metastasis in phyllodes tumor.

Sheet-like arrangement of tumor cells with indistinct cell borders forming a continuous cytoplasmic mass; characteristic of medullary carcinoma.

The functional unit of the breast, comprising the terminal duct and its associated lobular acini; the site of origin of most benign and malignant breast conditions

Humanised monoclonal antibody targeting the extracellular domain of HER2; standard of care for HER2-amplified breast carcinoma in both early and metastatic settings; must only be given when HER2 amplification is confirmed.

The gold-standard approach to breast lump evaluation integrating three independently graded investigations: clinical examination, radiological imaging (mammography or ultrasound), and pathological sampling (FNAC or core biopsy)

Breast carcinoma lacking ER, PR, and HER2 expression; ~15–20% of cases; aggressive high-grade tumour; basal-like phenotype; enriched for BRCA1 mutations; no targeted therapy except PARP inhibitors in BRCA-mutant cases.

Special-type invasive carcinoma: well-formed angulated open tubules lined by bland single-layer cells without myoepithelium, infiltrating desmoplastic stroma; Grade 1; ER+; excellent prognosis (>95% 10-year survival).