Introduction/Background Ataxia-telangiectasia is an autosomal recessive neurodegenerative disorder with immunodeficiency and an increased risk of developing cancer, caused by mutations in the ataxia-telangiectasia mutated (ATM) gene. Female carriers have an increased risk (20–30%) of developing breast cancer.

It is known that heterozygosity for a pathogenic ATM variant is present in 1%–2% of the adult population.

Methodology Retrospective observational study. Review of patients followed in the inherited cancer unit at Gregorio Marañón University General Hospital between 1stJanuary 2012 until 28thFebruary 2020.

The statistical analysis was carried out using SPSS 26.0.

Results During the indicated period, we followed 333 patients with confirmed genetic mutations that predispose to developing gynaecological cancer. Of the total, 1.5% (5/333) were carriers of a pathogenic ATM mutation and 0.6% (2/333) of a variant of uncertain meaning ATM mutation.

Within the cohort of patients carrying a pathogenic ATM mutation, all of them had family history of breast cancer and one also of ovarian cancer. 3/5 of the patients were diagnosed with breast cancer at 38, 40 and 48 years old, respectively. One of them, had a second contralateral breast cancer at 58 years old.

The histology of the primary breast cancer was: ductal carcinoma in situ, invasive ductal carcinoma and invasive lobular carcinoma. Tumor stage was 0 in one case and stage I in two cases. Primary treatment was surgery in all patients: unilateral mastectomy with homolateral axillary lymphadenectomy in one patient and conservative surgery with selective sentinel lymph node biopsy in the other 2. Adjuvant treatment was only needed in 2 patients: radiation therapy and hormone therapy in one case and radiation therapy, chemotherapy and hormone therapy in the other.

Characteristics of these patients are summarized in table 1.

Conclusion Patients carrying ATM mutations have a moderate-high risk of developing breast cancer and should be followed in specialized hereditary cancer units, in tertiary hospitals.

Disclosures No conflicts of interest to disclose.