Breast development and pathology
Breast: development, structure, blood supply, lymph drainage and common pathology
Breast anatomy for FCPS Part 1: milk line, position, Cooper's ligaments, arteries, nerves and lymph drainage to axillary and internal mammary nodes. Also covers mastitis, benign breast disease, carcinoma types, BRCA genes and nerve injury at axillary surgery.
One of the most tested topics in past papers
Development
- Arises from ectodermal mammary ridges (milk lines) running from axilla to groin in weeks 4–6; only the pectoral part normally persists. Glandular epithelium is ectodermal; the stroma is mesodermal.
- Solid buds canalise to form 15–20 lactiferous ducts; the nipple pit everts around birth (failure gives an inverted nipple).
| Anomaly | Meaning |
|---|---|
| Polythelia | Extra nipple along the milk line (commonest anomaly) |
| Polymastia | Extra breast tissue, commonest in the axilla; swells in pregnancy and may leak milk |
| Amastia, athelia | Absent breast or nipple |
| Poland syndrome | Absent sternocostal pectoralis major, hypoplastic breast, ipsilateral short webbed fingers |
- Newborns of either sex may have breast swelling with milky secretion (maternal oestrogen, then prolactin action when oestrogen falls).
- Thelarche (Tanner 2 breast bud) is usually the first sign of puberty in girls. Oestrogen drives duct proliferation and fat deposition; progesterone drives lobules and alveoli. Breasts and pubic hair in a young girl suggest a source of oestrogen, such as a granulosa cell tumour.
Position and structure
- Base extends from the 2nd to 6th rib and from the sternal edge to the midaxillary line; two-thirds lie on pectoralis major, the lower lateral third on serratus anterior and a little on the external oblique aponeurosis.
- The axillary tail passes through the deep fascia into the axilla.
- Retromammary space: loose areolar tissue between the breast and pectoral fascia lets the breast glide; a cancer that becomes fixed when pectoralis contracts has invaded the pectoral fascia.
- 15–20 lobes, each drained by one lactiferous duct with a lactiferous sinus beneath the areola.
- Terminal duct lobular unit (TDLU): the functional unit and site of most carcinomas. Ducts have luminal cells over myoepithelial cells on a basement membrane.
- Suspensory ligaments of Cooper run from the dermis to the deep fascia.
| Sign | Mechanism |
|---|---|
| Skin dimpling | Tumour shortens Cooper's ligaments |
| Peau d'orange | Dermal lymphatics blocked; skin oedema around tethered hair follicles |
| Nipple retraction | Tumour pulls lactiferous ducts |
- In the male the nipple lies at the 4th intercostal space (T4 dermatome).
- The upper outer quadrant has the most glandular tissue, so most cancers arise there.
Blood supply and nerves
| Source | Supplies |
|---|---|
| Internal thoracic perforators (2nd–4th spaces) | Medial part (main supply, about 60%) |
| Lateral thoracic artery | Lateral part |
| Thoracoacromial (pectoral branch) | Deep upper part |
| Posterior intercostal (lateral mammary branches) | Deep lateral part |
- Intercostal veins connect with the vertebral venous plexus (Batson), so breast cancer reaches the vertebrae without lung or liver deposits.
- Nerves: anterior and lateral cutaneous branches of T2–T6; the nipple is supplied mainly by the lateral cutaneous branch of the 4th intercostal nerve. Secretion is hormonal, not neural.
Lymph drainage
- About 75% to the axillary nodes, first the anterior (pectoral) group along the lateral thoracic vessels; the upper outer quadrant drains here and to apical nodes.
- Medial quadrants: also to parasternal (internal mammary) nodes beside the internal thoracic vessels.
- Subareolar plexus (Sappey): tracer injected here finds the sentinel node.
- Other routes: across the midline to the opposite breast; from the lower inner part through the rectus sheath to subperitoneal and hepatic lymphatics.
| Axillary group | Location |
|---|---|
| Anterior (pectoral) | Lateral thoracic vessels, lower border of pectoralis minor |
| Posterior (subscapular) | Subscapular vessels on the posterior wall |
| Lateral (humeral) | Along the axillary vein |
| Central | Axillary fat, near the intercostobrachial nerve |
| Apical | Apex of the axilla; drain to the subclavian lymph trunk |
| Interpectoral (Rotter's) | Between pectoralis major and minor |
- Surgical levels by pectoralis minor: level I lateral (below), level II behind, level III medial (apical).
Nerves and flaps at surgery
- Long thoracic nerve (C5–C7) on serratus anterior on the medial axillary wall: injury causes winging of the scapula and loss of overhead abduction, because serratus anterior rotates the scapula for abduction above 90 degrees.
- Thoracodorsal nerve (C6–C8) with the subscapular vessels: injury weakens latissimus dorsi.
- Intercostobrachial nerve (T2): numbness of the inner upper arm after clearance.
- TRAM or DIEP flap from the lower abdomen: a free flap needs the deep inferior epigastric artery anastomosed at the chest; a pedicled TRAM survives on the superior epigastric. Latissimus dorsi flap depends on the thoracodorsal artery.
Inflammatory and benign conditions
| Condition | Key features |
|---|---|
| Lactational mastitis and abscess | Milk stasis plus skin bacteria (Staphylococcus aureus) through a cracked nipple; red, hot, wedge-shaped; keep feeding or expressing |
| Galactocele | Milk-filled cyst after stopping breastfeeding; aspirate gives thick creamy milk |
| Fat necrosis | After trauma or surgery; saponified fat, foamy macrophages, calcification; mimics cancer |
| Tuberculous mastitis | Painful lump, sinuses, axillary nodes; caseating granulomas with Langhans giant cells |
| Silicone implant leak | Foreign-body giant cells and macrophages around refractile material |
| Fibrocystic change | Cyclical lumpy tenderness; straw-coloured cysts with apocrine metaplasia (granular pink cytoplasm), stromal fibrosis |
| Fibroadenoma | Commonest benign tumour under 35; mobile, rubbery |
| Intraductal papilloma | Commonest cause of bloody nipple discharge |
| Radial scar | Stellate spiculated lesion with a fibroelastic core and entrapped benign tubules; mimics cancer, so excised |
- Cancer risk in benign disease: non-proliferative change (cysts, apocrine metaplasia) no increase; usual ductal hyperplasia slight; atypical ductal or lobular hyperplasia moderate (about 4–5 times), the important finding.
Carcinoma
| Type | Features |
|---|---|
| Invasive carcinoma, no special type (ductal) | Commonest; nests, cords and glands in fibrous stroma; hard irregular lump |
| Invasive lobular | Single-file cells, loss of E-cadherin; often bilateral and multifocal |
| Mucinous (colloid) | Elderly; soft, well circumscribed; clusters floating in mucin lakes; good prognosis |
| Medullary pattern | Sheets with lymphocytes; linked with BRCA1 |
| Inflammatory | Red, warm, swollen breast with peau d'orange, no lump, no fever; tumour emboli in dermal lymphatics; poor prognosis |
- Grade describes the tumour's histology (tubule formation, nuclear pleomorphism, mitoses); stage describes size, nodes and metastasis. The number of involved axillary nodes is the strongest single prognostic factor.
- BRCA1 lies on chromosome 17 (17q21) and BRCA2 on chromosome 13 (13q12). Both are tumour suppressors in homologous recombination repair; BRCA1 also raises ovarian cancer risk. Young relatives with breast or ovarian cancer suggest these genes.
- Risk rises with oestrogen exposure (early menarche, late menopause, nulliparity). In HRT the added progestogen raises breast risk more than oestrogen alone, though it protects the endometrium.
- Tamoxifen blocks oestrogen receptors in breast but acts as an agonist in endometrium and liver: endometrial carcinoma and venous thrombosis are the important side effects.
Remember Medial breast: internal thoracic artery and parasternal nodes; lateral breast: lateral thoracic artery and axillary nodes.
Exam trap Levels are defined by pectoralis minor, not pectoralis major; nodes behind it are level II.
Exam trap A red, swollen, non-lactating breast that does not respond to antibiotics is inflammatory carcinoma until proved otherwise.
How FCPS asks about this
- Adult breast lies over: pectoralis major (2nd–6th ribs) and serratus anterior, with the axillary tail in the axilla.
- Main lymph drainage: axillary nodes, first the anterior (pectoral) group; medial quadrants also to internal mammary nodes.
- Vertebral metastasis: through intercostal veins to the vertebral venous plexus.
- Loss of overhead abduction after mastectomy: long thoracic nerve injury, serratus anterior paralysis.
- Duct proliferation and fat deposition: oestrogen; lobules and alveoli, progesterone.
- BRCA1 chromosome: 17; BRCA2, 13.
- Commonest cause of bloody nipple discharge: intraductal papilloma.
Test yourself on this topic
5 of the 60 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
During a mastectomy, the surgeon dissects the base of the breast off the chest wall. Medially and centrally the base rests on the fascia over pectoralis major. On the fascia of which muscle does its lower lateral part lie?
Answer: Serratus anterior
The base of the adult breast extends vertically from about the second to the sixth rib and horizontally from the lateral border of the sternum to the midaxillary line. About two-thirds of it lies on the pectoral fascia over pectoralis major, and the lower lateral third lies on the fascia over serratus anterior. A small inferior part may overlie the upper aponeurosis of external oblique, and the axillary tail passes into the axilla through an opening in the deep fascia.
Bed of the breast
- Ribs 2 to 6, sternum to midaxillary line
- Two-thirds on pectoralis major
- Lower lateral third on serratus anterior
Remember Breast bed: pectoralis major, then serratus anterior.
Exam trap Pectoralis minor lies deep to pectoralis major and does not form the breast bed.
Why the other options are wrong
- Pectoralis minor Lies deep to pectoralis major, not directly under the breast.
- Latissimus dorsi Forms the posterior axillary fold, behind the breast's lateral edge.
- Rectus abdominis Lies below the breast's lower edge.
- Subscapularis Lies on the posterior wall of the axilla.
A 55-year-old woman has a 2 cm area of pure ductal carcinoma in situ excised with clear margins. Sentinel node biopsy is not done. What feature of this lesion means it cannot have spread to lymph nodes?
Answer: The basement membrane is intact
In carcinoma in situ the malignant cells are confined within ducts by an intact basement membrane, with myoepithelial cells still present around them. Lymphatics and blood vessels lie in the stroma outside the basement membrane, so in situ cells have no access to them and cannot metastasise. Once cells breach the basement membrane the lesion becomes invasive and can spread. High-grade DCIS is larger and more likely to hide foci of invasion, which is why sentinel biopsy is sometimes added.
Carcinoma in situ
- Basement membrane intact
- Myoepithelial cells present
- No access to lymphatics
- Invasion means breach of membrane
Remember In situ means inside the membrane.
Exam trap Missed microinvasion in large high-grade DCIS can still involve nodes.
Why the other options are wrong
- The cells are low grade Grade affects recurrence and invasion risk, not access to lymphatics.
- There are no microcalcifications DCIS commonly shows calcifications.
- The tumour is oestrogen receptor-positive Receptor status does not prevent spread.
- Myoepithelial cells are absent Absent myoepithelium suggests invasion.
A screening programme in Lahore audits the sites of newly diagnosed breast carcinomas. In which part of the breast do most of these cancers arise, and why?
Answer: Upper outer quadrant, as it has most gland
About half of breast carcinomas arise in the upper outer quadrant, including the axillary tail. This is simply because this quadrant contains the largest volume of glandular tissue (terminal duct lobular units), from which carcinomas arise. Tumours here drain mainly to the anterior (pectoral) axillary nodes. The central (subareolar) region is the next most common site.
Site of breast cancer
- Commonest: upper outer quadrant
- Because it has most glandular tissue
- Includes the axillary tail
Remember Most gland, most cancer: upper outer.
Exam trap The axillary tail belongs to the upper outer quadrant and is easily missed.
Why the other options are wrong
- Nipple area, as most ducts open there The central region is the second most common site.
- Lower inner quadrant, as it has least fat The least common site.
- Upper inner quadrant, near internal thoracic Less glandular than the upper outer quadrant.
- Lower outer quadrant, near the inframammary fold Uncommon site.
Several years after a right mastectomy, a woman whose axillary nodes were heavily involved and treated with radiotherapy develops a nodule in the medial part of her left breast. How can tumour cells reach the opposite breast when the usual drainage is blocked?
Answer: Superficial lymphatics cross the midline
The superficial lymphatics of the breast skin communicate across the midline with those of the opposite breast. When the axillary route is obstructed by tumour, surgery or radiotherapy, lymph can be diverted through these channels, carrying tumour cells to the medial part of the opposite breast and axilla. Similar diversion can take lymph to the abdominal wall.
Contralateral spread
- Skin lymphatics cross midline
- Opens when axilla is blocked
- Reaches medial opposite breast
Remember Blocked axilla, lymph crosses the chest.
Exam trap Do not forget lymphatic diversion when the normal route is blocked.
Why the other options are wrong
- Thoracic duct carries lymph to the left Ends in the left venous angle; it does not drain to the breast.
- Internal thoracic veins join across the sternum Veins do not explain spread into breast tissue.
- Pectoral nodes drain to the opposite side Pectoral nodes drain to the central and apical nodes of the same side.
- Through the subperitoneal lymphatic plexus Leads to the abdomen, not the other breast.
A screening mammogram in a 49-year-old woman shows a 1.2 cm stellate lesion with long radiating spicules and a central lucent area. Excision shows a central fibroelastic core with entrapped benign tubules and radiating ducts with no malignant cells. What is the diagnosis?
Answer: Radial scar
A radial scar (complex sclerosing lesion) is a benign lesion with a central fibroelastic core that entraps small tubules, surrounded by radiating ducts and lobules. On mammography it forms a spiculated, star-shaped density that mimics carcinoma, often with a lucent centre. Because it cannot be distinguished reliably from cancer on imaging, it is excised or extensively sampled. Tubular carcinoma also has tubules but they are infiltrating and lack myoepithelial cells.
Radial scar
- Stellate lesion mimicking cancer
- Central fibroelastic core
- Entrapped benign tubules
- Needs excision or sampling
Remember A benign star that looks malignant.
Exam trap Spiculation on a mammogram is not diagnostic of cancer.
Why the other options are wrong
- Invasive tubular carcinoma Has malignant angulated tubules without myoepithelium.
- Fat necrosis Usually follows trauma and shows oil cysts and foamy macrophages.
- Sclerosing lymphocytic lobulitis Occurs in long-standing diabetes with lymphocytes around lobules.
- Fibroadenoma A rounded, well-circumscribed lump, not stellate.
Where this sits in the CPSP syllabus
- Obstetrics & Gynaecology, Paper 2: Abdominal wall and breast, Breast: development, structure, blood supply and lymph drainage