Low-grade triple-negative breast carcinomas is a descriptive term that could be used as a diagnostic term in a core needle biopsy if a specific subtype may not be established, referring the definitive diagnosis to the study of the surgical specimen. A correct diagnosis of a specific histopathological subtype is possible in certain cases and it allows adequate treatment within a multidisciplinary breast-unit in an increasingly frequent, neoadjuvant regimens context. It is essential to distinguish clearly between low-grade triple-negative breast cancer and others, as they have a different prognosis and require different therapeutic management during its evolution as a disease.
Low-grade triple-negative breast carcinomas are negative for estrogen receptors, progesterone receptors and HER2 (Human Epidermal Growth Factor Receptor 2), they have low proliferative indexes and a characteristic morphological and immunohistochemically profile.
They show a great molecular heterogeneity and stablishing the transcriptional or intrinsic subtypes is not yet included in daily clinical practice. As a group, they have a relatively indolent course; despite the fact they usually show poor responses to conventional chemotherapy. For this reason, the main problem with this group of tumors consists of not recognizing it as such and applying an inadequate treatment, especially an ineffective chemotherapy without an adequate cost/benefit ratio.
Although there is not enough evidence in some subtypes, it seems reasonable to consider these tumors as a group with characteristic genetic alterations and low response rates to conventional chemotherapy, partly due to a low proliferative index. Surgical treatment could be curative in certain cases, especially those cases diagnosed in early stages. Conventional chemotherapy would not be used in those cases that will not going to obtain enough benefit, doing less harm to the patient. Furthermore, the detection of the expression of some biomarkers (PDL1, NTRK) could be used to carry out a targeted treatment. Finally, the metaplastic subtype is radiosensitive.
