Photomicrographs demonstrating examples of RRM1 and RRM2B status in invasive breast tumors. Samples were analyzed by FISH using Texas Red (RRM1 or RRM2B) and fluorescein isothiocyanate (chromosome 11and 8) labeled probes (Leica DM microscope, 100 × objective, oil emulsion). (A) Breast tumor with RRM1 gene deletion (FISH ratio < 0.8). (B) Breast tumor with RRM2B gene amplification (FISH ratio ≥ 2.0). Abbreviation: FISH, fluorescence in situ hybridization; RRM1, ribonucleotide reductase M1 subunit; RRM2B, ribonucleotide reductase M2B subunit.