{"entity":{"id":"terminal-duct-lobular-unit","kind":"term","name":"Ducts, lobules and the terminal duct lobular unit","aka":["terminal duct lobular unit","TDLU","ducts and lobules","milk ducts","lobule","breast lobule","breast duct","ductal","lobular","breast anatomy","mammary gland"],"tldr":"The breast is a tree: fifteen to twenty branching duct systems, each ending in a cluster of milk-making sacs called a lobule. Almost every breast cancer starts at the junction between the smallest ducts and their lobule, which is why the two commonest kinds are called ductal and lobular.","summary":"Each breast holds fifteen to twenty lobes, and each lobe is a branching system of ducts that ends in lobules, the grape-like clusters of acini that make milk. The junction where the smallest duct meets its lobule is the terminal duct lobular unit, and it is where almost all breast carcinoma and almost all of the benign lesions that mimic it arise. The rest of the breast is fat, fibrous tissue and skin, with lymphatic channels that drain mostly to the axilla and, from the inner part of the breast, to the internal mammary chain behind the ribs, which is why the armpit is examined and scanned at the first appointment.\n\nThe names of the two commonest types come from this anatomy, but they are misleading in an instructive way. Invasive carcinoma of no special type, still widely called invasive ductal carcinoma, does not arise in the large ducts, and invasive lobular carcinoma does not arise in the lobules: both begin in the terminal duct lobular unit, and the words describe what the tumour looks like down the microscope rather than where it started. The real difference is E-cadherin, the protein that glues cells to their neighbours. Lobular cancers have lost it, so they infiltrate in single files rather than forming a mass, which is why they are harder to feel, harder to see on a mammogram and harder to measure before surgery.\n\nMen have ducts too, and a small amount of breast tissue behind the nipple, but generally lack the terminal lobules, which is the reason the male breast cancer page gives for male breast cancer being almost always of no special type and lobular carcinoma in a man being very rare. The breast changes throughout life: it is densest in young women, involutes after the menopause, and density itself both raises risk and hides cancers on a mammogram.","asOf":"2026-09-25","wikipedia":"https://en.wikipedia.org/wiki/Terminal_duct_lobular_unit","links":[{"label":"Tan et al., Histopathology 2020: the 2019 WHO classification of tumours of the breast (5th edition)","url":"https://doi.org/10.1111/his.14091"},{"label":"Cancer Research UK: types of breast cancer","url":"https://www.cancerresearchuk.org/about-cancer/breast-cancer/types"},{"label":"Royal College of Pathologists G148: dataset for histopathological reporting of breast disease in surgical excision specimens of breast cancer, version 3, November 2024 (full review due November 2026)","url":"https://www.rcpath.org/resourceLibrary/g148-dataset-for-histopathological-reporting-of-breast-disease-in-surgical-excision-specimens-of-breast-cancer.html"}],"tags":[],"related":["carcinoma-in-situ","lymph-node-status","mammography","sentinel-lymph-node-biopsy"],"cancers":["breast-cancer","invasive-breast-carcinoma-no-special-type","invasive-lobular-carcinoma","male-breast-cancer"],"sections":["diagnostics"],"technologies":[],"targets":[],"drugs":[],"companies":[],"institutions":[],"pathways":[],"terms":["who-breast-classification","carcinoma-in-situ","lymph-node-status"],"trials":[],"people":[],"bottlenecks":[],"keyPapers":[],"journals":[],"dependsOn":[],"notes":[],"category":"Anatomy"},"route":"/terms/terminal-duct-lobular-unit/","neighbours":{"term":[{"id":"carcinoma-in-situ","kind":"term","name":"Carcinoma in situ (CIS)","route":"/terms/carcinoma-in-situ/"},{"id":"lymph-node-status","kind":"term","name":"Lymph node status (node-positive / node-negative)","route":"/terms/lymph-node-status/"},{"id":"sentinel-lymph-node-biopsy","kind":"term","name":"Sentinel node biopsy","route":"/terms/sentinel-lymph-node-biopsy/"},{"id":"who-breast-classification","kind":"term","name":"The WHO classification of breast tumours, and what the 6th edition changed","route":"/terms/who-breast-classification/"}],"technology":[{"id":"mammography","kind":"technology","name":"Mammography & tomosynthesis","route":"/technologies/mammography/"}],"cancer":[{"id":"breast-cancer","kind":"cancer","name":"Breast cancer (all types)","route":"/cancers/breast-cancer/"},{"id":"ductal-carcinoma-in-situ","kind":"cancer","name":"Ductal carcinoma in situ (DCIS)","route":"/cancers/ductal-carcinoma-in-situ/"},{"id":"invasive-breast-carcinoma-no-special-type","kind":"cancer","name":"Invasive breast carcinoma of no special type (invasive ductal carcinoma)","route":"/cancers/invasive-breast-carcinoma-no-special-type/"},{"id":"invasive-lobular-carcinoma","kind":"cancer","name":"Invasive lobular carcinoma of the breast","route":"/cancers/invasive-lobular-carcinoma/"},{"id":"lobular-carcinoma-in-situ","kind":"cancer","name":"Lobular carcinoma in situ (LCIS)","route":"/cancers/lobular-carcinoma-in-situ/"},{"id":"male-breast-cancer","kind":"cancer","name":"Male breast cancer","route":"/cancers/male-breast-cancer/"}],"section":[{"id":"diagnostics","kind":"section","name":"Diagnostics & Biomarkers","route":"/fronts/diagnostics/"}]}}