Triple-negative breast cancer (sometimes abbreviated TNBC) refers to any breast cancer that does not express the genes for estrogen receptor (ER), progesterone receptor (PR) or Her2/neu. This makes it more difficult to treat since most chemotherapies target one of the three receptors, so triple-negative cancers often require combination therapies. Triple negative is sometimes used as a surrogate term for basal-like; however, more detailed classification may provide better guidance for treatment and better estimates for prognosis.
Contents
- Cause
- Classification
- Treatment
- Epidemiology
- Clinical researchtrials
- Pre clinical researchspeculations
- References
Triple-negative breast cancers comprise a very heterogeneous group of cancers. There are conflicting information over prognosis for the various subtypes but it appears that the Nottingham prognostic index is valid and hence general prognosis is rather similar with other breast cancer of same stage, except that more aggressive treatment is required. Some types of triple-negative breast cancer are known to be more aggressive with poor prognosis, while other types have very similar or better prognosis than hormone receptor positive breast cancers. Pooled data of all triple-negative subtypes suggest that with optimal treatment 20-year survival rates are very close to those of hormone positive cancer.
Triple-negative breast cancers have a relapse pattern that is very different from hormone-positive breast cancers: the risk of relapse is much higher for the first 3–5 years but drops sharply and substantially below that of hormone-positive breast cancers after that. This relapse pattern has been recognized for all types of triple-negative cancers for which sufficient data exists although the absolute relapse and survival rates differ across subtypes.
Cause
One known cause of triple negative breast cancer is germline mutations. These are alterations within the heritable lineage that is being passed down to the offspring. 15% of TNBC can be traced back to germline mutations that are within the BRCA1 and BRCA2 genes (Song 2014). These genes were identified as high risk for triple negative due to their high predisposition for cancers of the breasts, ovaries, pancreas, and prostate (Pruss 2014). Changes or mutations in 19p13.1 and MDM4 loci have been associated with Triple negative, but not other forms of breast cancer, thus Triple Negative can be distinguished from other breast cancer subtypes by a unique pattern of common and rare germline alterations (Kristen 2013).
Classification
Triple-negative breast cancers (TNBC) are sometimes classified into "basal-type" and other cancers; however, there is no standard classification scheme. Basal type cancers are frequently defined by cytokeratin 5/6 and EGFR staining. However, no clear criteria or cutoff values have been standardized yet. About 75% of basal-type breast cancers are triple negative.
Some TNBC overexpresses epidermal growth factor receptor (EGFR). Some TNBC over expresses transmembrane glycoprotein NMB (GPNMB).
Upon histologic examination, triple-negative breast tumors mostly fall into the categories of secretory cell carcinoma or adenoid cystic types (both considered less aggressive); medullary cancers and grade 3 invasive ductal carcinomas with no specific subtype; and highly aggressive metastatic cancers. Medullary TNBC in younger women are frequently BRCA1-related.
Rare forms of triple-negative breast cancer are apocrine and squamous carcinoma. Inflammatory breast cancer is also frequently triple negative.
Many proteins such as Caveolin 1/2, Survivin are researched as possible classification or prognostic factors.
Treatment
Standard treatment is surgery with adjuvant chemotherapy and radiotherapy. As a variation neoadjuvant chemotherapy is very frequently used for triple-negative breast cancers. This allows for a higher rate of breast-conserving surgeries and by evaluating the response to the chemotherapy gives important clues about the individual responsiveness of the particular cancer to chemotherapy.
In addition to chemotherapy, an additive called Didox can be added to aid in the reduction of drug resistance and further treatment efforts. Didox is used to inhibit ribonucleotide reductase M2 (RRM2) which contributes to the cells resistance of the chemotherapy treatment resulting in a large number of relapse (Wilson 2016). RRM2 is upregulated within these specific Triple Negative cancer cells leading to a higher rate of drug resistance and inability to slow or stop the tumor progression which leads to more aggressive forms of triple negative breast cancer that are often fatal (Wilson 2016).
TNBCs are generally very susceptible to chemotherapy. In some cases, however, early complete response does not correlate with overall survival. This makes it particularly complicated to find the optimal chemotherapy. Adding a taxane to the chemotherapy appears to improve outcome substantially.
BRCA1-related triple-negative breast cancer appear to be particularly susceptible to chemotherapy including platinum-based agents and taxanes.
Epidemiology
Triple-negative breast cancer accounts for approximately 15%-25% of all breast cancer cases. The overall proportion of TNBC is very similar in all age groups. Younger women have a higher rate of basal or BRCA related TNBC while older women have a higher proportion of apocrine, normal-like and rare subtypes including neuroendocrine TNBC.
Among younger women, African American and Hispanic women have a higher risk of TNBC, with African Americans facing worse prognosis than other ethnic groups.
In 2009, a case-control study of 187 triple-negative breast cancer patients described a 2.5 increased risk for triple-negative breast cancer in women who used oral contraceptives (OCs) for more than one year compared to women who used OCs for less than one year or never. The increased risk for triple-negative breast cancer was 4.2 among women 40 years of age or younger who used OCs for more than one year, while there was no increased risk for women between the ages of 41 and 45. Also, as duration of OC use increased, triple-negative breast cancer risk increased.
Clinical research/trials
Angiogenesis and EGFR (HER-1) inhibitors are frequently tested in experimental settings and have shown efficacy. Treatment modalities are not sufficiently established for normal use, and it is unclear in which stage they are best used and which patients would profit.
By 2009 A number of new strategies for TNBC were being tested in clinical trials, including the PARP inhibitor BSI 201, NK012.
A novel antibody-drug conjugate known as Glembatumumab vedotin (CDX-011), which targets the protein GPNMB, has also shown encouraging clinical trial results in 2009.
PARP inhibitors had shown some promise in early trials but failed in some later trials.
Nov 2013: An accelerated approval Phase II clinical trial (METRIC) investigating glembatumumab vedotin versus capecitabine has begun, expected to enroll 300 patients with GPNMB-expressing metastatic TNBC.
Three early stage trials reported TNBC results in June 2016, for IMMU-132, Vantictumab, and atezolizumab in combination with the chemotherapy nab-paclitaxel.
Pre-clinical research/speculations
Triple-negative breast cancers (TNBC) have, on average, significantly higher fluorine-18 fluorodeoxyglucose (FDG) uptake (measured by the SUVmax values) compared with uptake in ER+/PR+/HER2- tumors using fluorine-18 fluorodeoxyglucose-positron emission tomography (FDG-PET). It is speculated that enhanced glycolysis in these tumors is probably related to their aggressive biology.
The widely used diabetes drug, metformin, holds promise for the treatment of triple-negative breast cancer. In addition metformin may influence cancer cells through indirect (insulin-mediated) effects, or it may directly affect cell proliferation and apoptosis of cancer cells. Epidemiologic and preclinical lab studies indicate that metformin has anti-tumor effects, via at least two mechanisms, both involving activation of the AMP-activated protein kinase (AMPK). A large-scale phase III trial of metformin in the adjuvant breast cancer setting is being planned in 2009.
Triple-negative breast cancer cells rely on glutathione-S-transferase Pi1, and an inhibitor (LAS17) shows encouraging results in a pre-clinical study