Genomic classifications and radiotherapy for breast cancer

Local Treatment of Triple-Negative Breast Cancer

ABSTRACT

Triple-negative breast cancer, compared with other molecular subtypes, poses particular challenges for optimizing the timing and the extent of locoregional treatments. In the past, the combination of increased rates of both locoregional and distant recurrences led to a preference of radical surgery and extensive radiation therapy; however, since the introduction of more effective chemotherapy, a sharp de-escalation in the extent of locoregional treatments followed. Current evidence confirms that less aggressive surgery in combination with tailored radiation therapy offers improved oncological outcomes combined with better quality of life. However, further research is required to optimize locoregional treatments, considering the significant heterogeneity in biological behavior and tumor response to systemic treatments.

The prognosis comparison of different molecular subtypes of breast tumors after radiotherapy and the intrinsic reasons for their distinct radiosensitivity

Radiotherapy can increase the cell cycle arrest that promotes apoptosis, reduces the risk of tumor recurrence and has become an irreplaceable component of systematic treatment for patients with breast cancer. Substantial advances in precise radiotherapy unequivocally indicate that the benefits of radiotherapy vary depending on intrinsic subtypes of the disease; luminal A breast cancer has the highest benefit whereas human epidermal growth factor receptor 2 (HER2)-positive and triple negative breast cancer (TNBC) are affected to a lesser extent irrespective of the selection of radiotherapy strategies, such as conventional whole-breast irradiation (CWBI), accelerated partial-breast irradiation (APBI), and hypofractionated whole-breast irradiation (HWBI). The benefit disparity correlates with the differential invasiveness, malignance, and radiosensitivity of the subtypes. A combination of a number of molecular mechanisms leads to the strong radioresistant profile of HER2-positive breast cancer, and sensitization to irradiation can be induced by multiple drugs or compounds in luminal disease and TNBC. In this review, we aimed to summarize the prognostic differences between various subtypes of breast tumors after CWBI, APBI, and HWBI, the potential reasons for drug-enhanced radiosensitivity in luminal breast tumors and TNBC, and the robust radioresistance of HER2-positive cancer.

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Tailoring radiotherapy according to cancer subtypes

Radiotherapy is able to improve locoregional control in breast cancer patients both after breast conserving surgery or mastectomy, with positive impact in high-risk patients for long-term survival. Recent advances in the precision of radiotherapy were based on the choice of the appropriate fractionation and technique. But the concept of adaptive radiotherapy is not only technical, and includes the biologic characterisation of the breast tumor. The knowledge that different subtypes of breast cancer can have distinct locoregional patterns of recurrence is consisted in the literature data. Luminal A tumor are at the lower risk of locoregional failure, and HER2 positive and triple negative at the higher risk. More evidence in the use of molecular markers for adjuvant radiotherapy can held in choosing the best treatment on individual. The combination of radiotherapy with molecular targeted therapies may enhance radiosensitivity, thus increasing the cytotoxic effects and improving treatment response. The appropriateness of an alternative fractionation, partial breast irradiation, intensification or de-intensification approaches, could be assessed better according the stratification of the risk categories.

Circadian disruption and breast cancer: an epigenetic link?

Breast cancer is already the most common malignancy affecting women worldwide, and evidence is mounting that breast cancer induced by circadian disruption (CD) is a warranted concern. Numerous studies have investigated various aspects of the circadian clock in relation to breast cancer, and evidence from these studies indicates that melatonin and the core clock genes can play a crucial role in breast cancer development. Even though epigenetics has been increasingly recognized as a key player in the etiology of breast cancer and linked to circadian rhythms, and there is evidence of overlap between epigenetic deregulation and breast cancer induced by circadian disruption, only a handful of studies have directly investigated the role of epigenetics in CD-induced breast cancer. This review explores the circadian clock and breast cancer, and the growing role of epigenetics in breast cancer development and circadian rhythms. We also summarize the current knowledge and next steps for the investigation of the epigenetic link in CD-induced breast cancer.

Ionizing radiation-induced DNA injury and damage detection in patients with breast cancer

Breast cancer is the most common malignancy in women. Radiotherapy is frequently used in patients with breast cancer, but some patients may be more susceptible to ionizing radiation, and increased exposure to radiation sources may be associated to radiation adverse events. This susceptibility may be related to deficiencies in DNA repair mechanisms that are activated after cell-radiation, which causes DNA damage, particularly DNA double strand breaks. Some of these genetic susceptibilities in DNA-repair mechanisms are implicated in the etiology of hereditary breast/ovarian cancer (pathologic mutations in the BRCA 1 and 2 genes), but other less penetrant variants in genes involved in sporadic breast cancer have been described. These same genetic susceptibilities may be involved in negative radiotherapeutic outcomes. For these reasons, it is necessary to implement methods for detecting patients who are susceptible to radiotherapy-related adverse events. This review discusses mechanisms of DNA damage and repair, genes related to these functions, and the diagnosis methods designed and under research for detection of breast cancer patients with increased radiosensitivity.