In order to define candidate regions that may harbor specific genes relevant to breast cancer development, we identified the smallest aUPD regions at chromosome 3p21.31 (TUSC4, SEMA3F, SEMA3B, RASSF1, MAPKAPK3, HYAL1, HYAL2, FUS), 3p26.2-p26.1 (LRRN1, SETMAR, SUMF1), 3p26.1 (GRM7), 11q22.3 (CASP, CASP4, CASP5, CASP12, COP1, CARD16, CARD18, GRIA4) (Table 3) in TN breast cancer samples. The gene discussed is LRRN1; the disease is breast cancer.