Introduction/Background NBN/NBS1 (nibrin), encoded by the NBN gene (chromosome 8q21), is involved in the regulation of the cell cycle and DNA double-stranded break repair mechanism. Mutations in NBN gene seem to be involved in susceptibility to different types of cancer, including breast cancer.

Methodology A retrospective observational study was carried out on 552 patients with confirmed genetic mutations that predispose to develop gynaecological cancer from the Hereditary Cancer Unit of Gregorio Marañón University General Hospital from 1st January 2012 to 15th October 2023. The statistical analysis was carried out using SPSS v.22.0.

Results Of the total patients included in the current study (n = 552), 1.27% (7/552) carried NBN mutations. Within the cohort of patients carrying NBN mutations, 57% (4/7) had a family history of breast cancer: i) 28.5% (2/7) in first-degree, and ii) 28.5% (2/7) in second-degree. In addition, 28.5% (2/7) debuted with breast cancer with infiltrating ductal carcinoma. Epidemiological characteristics are summarized in table 1.

Discussion There are numerous variants in DNA double-strand break repair genes that have been shown to be involved in increased risk of breast cancer, included mutations in NBN. According to 2017 NCCN guidelines, from 40 years old, annual mammography is recommended as well as an annual breast MRI with contrast, without evidence of risk of ovarian cancer.

However, in new 2023 NCCN guidelines, mutations in NBN aren´t listed as pathogenic. As well as ESMO guidelines 2022.

It´s recommended that they continue routine or adjusted breast screening according to their family and personal history. Due to these new recommendations, we´ve eliminated the routine analysis of NBN in our multigenetic panel.

Conclusion According our study, there were 2/7 patients with breast cancer, only one under 40 years old. Given the small sample size, we cannot conclude with certainty whether the risk of breast cancer was increased or not in our cohort.

Disclosures None.