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Radiation therapy is an essential intervention used in the treatment plan of more than half of cancer patients. With the increasing use of hypofractionated radiation regimens, concurrent use of radiation and chemotherapy, targeted agents and immunotherapy, the risk of radiation-induced toxicities is increased. Hematopoietic toxicity caused by radiation limits a patient’s options for subsequent systemic therapy. However, much remains unknown about the molecular underpinnings responsible for radiation-induced hematopoietic toxicity. MicroRNA (miRNA) are small, non-coding RNA involved in post-transcriptional regulation of gene expression and are associated with essential cellular processes. miR-21 is a potent oncomiR that is dysregulated in a significant fraction of human malignancies, and its overexpression is linked to poor overall survival, chemoresistance, and radioresistance in several human cancers. However, the contribution of miR-21 in governing radiation sensitivity in normal, untransformed cells, and the impact of silencing this miRNA in normal tissues remains largely unexplored. We determined ionizing radiation significantly increased miR-21 levels in radio-sensitive tissues, but not in radio-insensitive tissues, suggesting it may have a critical function in the normal tissue response to radiation. To test this concept, we generated miR-21 knockout mice. Mice lacking one or both alleles of miR-21 showed reduced numbers of hematopoietic stem and progenitor cells (HSPCs) and increased sensitivity to an LD50/30 dose of total body irradiation (TBI) with evidence of bone marrow failure compared to wild-type mice. Transplantation of wild-type bone marrow into irradiated miR-21-deficient mice rescued the mice from death. Thus, our data identify miR-21 as a critical component of HSPC viability and essential for bone marrow recovery following irradiation. Further investigation is warranted to determine if miR-21 can be used to stratify patients at risk for hematopoietic toxicity following irradiation.

To determine the associated toxicity, tolerance, and safety of partial-breast reirradiation.Eligibility criteria included in-breast recurrence occurring1 year after whole-breast irradiation,3 cm, unifocal, and resected with negative margins. Partial-breast reirradiation was targeted to the surgical cavity plus 1.5 cm; a prescription dose of 45 Gy in 1.5 Gy twice daily for 30 treatments was used. The primary objective was to evaluate the rate of grade ≥3 treatment-related skin, fibrosis, and/or breast pain adverse events (AEs), occurring ≤1 year from re-treatment completion. A rate of ≥13% for these AEs in a cohort of 55 patients was determined to be unacceptable (86% power, 1-sided α = 0.07).Between 2010 and 2013, 65 patients were accrued, and the first 55 eligible and with 1 year follow-up were analyzed. Median age was 68 years. Twenty-two patients had ductal carcinoma in situ, and 33 had invasive disease: 19 ≤1 cm, 13 1 to ≤2 cm, and 1 2 cm. All patients were clinically node negative. Systemic therapy was delivered in 51%. All treatment plans underwent quality review for contouring accuracy and dosimetric compliance. All treatment plans scored acceptable for tumor volume contouring and tumor volume dose-volume analysis. Only 4 (7%) scored unacceptable for organs at risk contouring and organs at risk dose-volume analysis. Treatment-related skin, fibrosis, and/or breast pain AEs were recorded as grade 1 in 64% and grade 2 in 7%, with only 1 (2%) grade ≥3 and identified as grade 3 fibrosis of deep connective tissue.Partial-breast reirradiation with 3-dimensional conformal radiation therapy after second lumpectomy for patients experiencing in-breast failures after whole-breast irradiation is safe and feasible, with acceptable treatment quality achieved. Skin, fibrosis, and breast pain toxicity was acceptable, and grade 3 toxicity was rare.

In well-selected patients who choose to pursue breast conservation therapy (BCT) for early-stage breast cancer, partial breast irradiation (PBI) delivered externally or intraoperatively, may be a viable alternative to conventional whole breast irradiation. Two large, contemporary randomized trials have demonstrated breast intraoperative radiotherapy (IORT) to be noninferior to whole breast external beam radiotherapy (EBRT) when assessing for ipsilateral breast tumor recurrence in select patients. Additionally, IORT and other PBI techniques are likely to be more widely adopted in the future because they improve patient convenience by offering an accelerated course of treatment. Coupled with these novel techniques for breast radiotherapy (RT) are distinct toxicity profiles and unique cosmetic alterations that differ from conventional breast EBRT and have the potential to impact disease surveillance and patient satisfaction. This paper will review the level-one evidence for treatment efficacy as well as important secondary endpoints like RT toxicity, breast cosmesis, quality of life, patient satisfaction, and surveillance mammography following BCT with IORT.

Approximately one-third of all breast cancer patients experience local recurrence of their tumor after initial treatment. As initial treatment often employs the use of radiation therapy (RT), the standard of care for local breast cancer recurrence after initial breast conserving therapy has traditionally been surgical intervention with mastectomy. However, recent attempts to preserve the intact breast after recurrence with local excision have revealed a potential need for RT in addition to repeat breast conserving surgery as rates of local failure with resection alone remain high. Additionally, local recurrence following initial mastectomy and chest wall RT can be treated with reirradiation to increase local control. Repeating RT, however, in a previously irradiated area, is a complex treatment strategy, as the clinician must carefully balance maximizing treatment effectiveness while minimizing treatment-related toxicity. As a result, physicians have been hesitant to treat recurrent disease with repeat RT with limited data. Results from the current literature are promising and current clinical trials are underway to explore reirradiation modalities which will provide additional information on treatment-related toxicity and outcomes. This paper will review the current literature on repeat radiation therapy for locally recurrent breast cancer.

Metabolic syndrome, which can include weight gain and central obesity, elevated serum insulin and glucose, and insulin resistance, has been strongly associated with breast cancer recurrence and worse outcomes after treatment. Epidemiologic and prospective data do not show conclusive evidence as to which dietary factors may be responsible for these results. Current strategies employ low-fat diets which emphasize supplementing calories with increased intake of fruit, grain, and vegetable carbohydrate sources. Although results thus far have been inconclusive, recent randomized trials employing markedly different dietary strategies in noncancer patients may hold the key to reducing multiple risk factors in metabolic syndrome simultaneously which may prove to increase the long-term outcome of breast cancer patients and decrease recurrences. Since weight gain after breast cancer treatment confers a poor prognosis and may increase recurrence rates, large-scale randomized trials are needed to evaluate appropriate dietary interventions for our breast cancer patients.