What does triple-negative actually mean? The cancer cells lack the three receptors other breast cancers are treated through: oestrogen receptor under 1 percent of nuclei, progesterone receptor under 1 percent, and HER2 scored 0 or 1+, or 2+ without gene amplification. Each is measured on the biopsy by immunohistochemistry (ASCO/CAP 2020 and 2018; NICE NG101 1.3). A tumour with ER of 1 to 10 percent is reported as ER Low Positive and behaves like triple-negative disease (Yoder 2022; Acs 2024).
How common is it? About 10.8 percent of US breast cancers with a known subtype (SEER 21, 2019 to 2023) and around 15 percent on Cancer Research UK's page; roughly 12 percent in earlier US series (Howlader 2014). It is diagnosed younger: women under 40 have about 1.5 to 2 times the odds of a triple-negative diagnosis (Bauer 2007; Scott 2019).
Why is it more common in Black women? In the United States the rate is 25.7 per 100,000 non-Hispanic Black women against 13.0 for non-Hispanic White women (SEER 21), and in the UK POSH cohort 26.1 percent of Black against 18.6 percent of White young patients had triple-negative tumours (Copson 2014). Reproductive patterns (parity without breastfeeding raises ER-negative risk in African American women, Palmer 2014), ancestry and access all contribute; the causes are not settled (Howard and Olopade 2021).
Should I have a genetic test? NICE says yes for women under 50 with triple-negative disease even without a family history (NG101 1.3.6), and UK mainstream criteria extend testing to all triple-negative disease under 60 (Evans 2024); about 11 percent of unselected triple-negative patients carry a BRCA1 or BRCA2 mutation and 14.6 percent a mutation in one of 17 genes (Couch 2015). The result changes surgery options, opens olaparib after chemotherapy for high-risk early disease (NICE TA886) and matters for relatives.
Is it more dangerous than other breast cancers? Stage for stage, survival is lower: 78.7 percent five-year relative survival against 95.8 percent for hormone receptor-positive, HER2-negative disease in SEER, but 92.8 percent when found while localised. The risk of relapse is concentrated in the first three to five years and is low afterwards (Dent 2007), and a pathological complete response to chemotherapy before surgery carries an excellent outlook (Liedtke 2008; Cortazar 2014).
Why did my treatment start with chemotherapy rather than surgery? For tumours over 2 cm or with node involvement, chemotherapy with pembrolizumab is given first because the response at surgery predicts relapse and directs what follows, and because it raised five-year survival from 81.7 to 86.6 percent in KEYNOTE-522 (Schmid 2024). NICE recommends a platinum, a taxane and an anthracycline in that setting (NG101 1.8, 2025) and pembrolizumab with it (TA851).
Does hormone therapy or tamoxifen have any role? Not to treat triple-negative disease, which has no oestrogen receptor to block. As prevention, tamoxifen and anastrozole reduced ER-positive but not ER-negative breast cancer in the prevention trials (Cuzick 2015; Fisher 1998; Cuzick 2020), although tamoxifen after a first cancer was associated with fewer contralateral cancers in BRCA carriers (Phillips 2013).
Will screening pick it up? The NHS invites women from 50 to 71 every three years (NHS). Triple-negative cancers are less often screen-detected (29 percent against 48 percent, Lin 2012) because they arise younger and grow between rounds. Known BRCA carriers are offered annual MRI from 30 and mammography from 40 (NICE CG164); anyone with a new breast change should see a GP without waiting for the next screen.
What are the subtypes I might read about? Gene expressiondivides triple-negative disease into basal-like 1 and 2, mesenchymal and luminalandrogen receptor tumours (Lehmann 2016), which respond differently to chemotherapy (pathological complete response 41 percent for basal-like 1, 18 percent for basal-like 2, 29 percent for luminal androgen receptor) but are not used to choose treatment in the NHS. Special histological types such as adenoid cystic and secretory carcinoma are triple-negative but indolent and may need no chemotherapy (Cserni 2021). Each has a page linked from this record.
What is HER2-low and why does it matter if I am HER2-negative? HER2 1+, or 2+ without amplification, is called HER2-low; those tumours (63 of 557 patients in DESTINY-Breast04 had hormone receptor-negative disease) responded to trastuzumab deruxtecan, so the pathologist's distinction between 0 and 1+ now has a treatment consequence (Modi 2022; ASCO-CAP 2023).
Frequencies marked cBioPortal were computed from the public API on 24 September 2026 on receptor-defined triple-negative subsets of brca_tcga_pub (123 samples; the same patients read in brca_tcga_pan_can_atlas_2018), brca_metabric (320) and breast_msk_2018 (176), as sample-level counts of non-synonymous mutation, high-level amplification or deep deletion over the subset; they are not the papers' own percentages, which are quoted alongside.
Metastatic samples in breast_msk_2018 (85 of 176) and the 173-gene METABRIC panel make cross-cohort comparison approximate; TMB on the MSK panel is reported as a mutation count, not a per-megabase rate.
Machine-readable versions
The same record for scripts and assistants; checked 2026-09-24. Data CC BY-NC 4.0, attribute “Data from OnCo (onco.cc)”.