Table 2.

Summary of studies carried out that evaluated the risks associated with exposure to ionizing radiation, associated with radiotherapy, in carriers of mutations in the BRCA1 and BRCA2 genes.

Authors	Year	Sample Size (n)	Gene	Dose	Outcome
Broeks et al. [50]	2007	247 (169 treated with radiotherapy and 78 not treated)	BRCA1, BRCA2, CHEK and ATM	30.5–76 Gy	The risk of developing contralateral breast cancer after radiotherapy was higher for individuals carrying mutations in genes involved in DNA damage repair pathways.
Pierce et al. [51]	2010	655 carriers	BRCA1 and BRCA2	Not disclosed	The risk of developing contralateral breast cancer was higher for individuals undergoing BCS compared to individuals undergoing mastectomy. The risk in individuals undergoing adjuvant radiotherapy was not statistically significant.
Metcalfe et al. [52]	2011	810 carriers	BRCA1 and BRCA2	Not disclosed	The risk of developing contralateral breast cancer decreased with age at diagnosis, increasing with the number of first-degree relatives with the same diagnosis.
Bernstein et al. [53]	2013	1802 (603 with contralateral breast cancer and 1199 with unilateral breast cancer)	BRCA1 and BRCA2	1.1 Gy (range = 0.02–6.2 Gy)	The risk of developing contralateral breast cancer in carriers was four times greater, however, carriers undergoing radiation therapy for primary breast cancer did not have a significantly higher relative risk of contralateral breast cancer.
Schlosser et al. [54]	2020	230 carriers	BRCA1 and BRCA2	50 Gy (25 fractions, 2Gy per fraction (fx)) or 42.4 Gy for patients treated after 2010 (16 fractions, 2.65 Gy/fx) or 50.4 Gy for reconstructed or augmented breasts (28 fractions, 1.8 Gy/fx) or 45 Gy in 1.8 Gy/fx	Women with the mutation undergoing radiation therapy for breast cancer did not have a statistically significant risk of a second primary malignancy induced by exposure to ionizing radiation.