BRCA1 and thyroid cancer: However, functional evidence is lacking, and homologous recombination deficiency (HRD)-the hallmark of BRCA-driven cancers-has not been systematically assessed in <i>BRCA1</i>-associated SGTs.<h4>Case presentation</h4>We report a Colombian family segregating the <i>BRCA1</i> c.3331_3334delCAAG (p.Gln1111Asnfs*5) founder variant with phenotypic variability across four generations: gastric (31%), breast (37.5%), colorectal (19%), and thyroid cancers (12.5%).