The β isoform of the fibroblast growth factor receptor type 1 is selected for in increasingly metastatic cells and can be readily identified in patient tumor samples. (A) Schematic representation the FGFR1 transcript depicting the coding regions for the immunoglobulin (Ig), transmembrane (TM), and kinase domains. The location of the unique IIIb/IIIc primer sets (arrows) and the flanking primer set detecting the inclusion or exclusion of the α exon (arrows) are also indicated. (B) Expression of FGFR1 isoforms depicted in (A) were analyzed by RT-PCR in the nonmetastatic normal mammary epithelial (NME) cells and their lung metastatic (LM) and isogenic NME-LM2 counterparts before (ns) and after a 48-hour treatment with 5 ng/ml transforming growth factor β (TGF). (C) Luminal MCF-7, T47D, MDA-MB-361 and ZR-75-1 and basal MDA-MB-231 and BT549 human breast cancer cells were analyzed for inclusion or exclusion of the α exon of FGFR1. The estrogen-independent T47D-C42W cells were also analyzed. Data in (B) and (C) are representative of three independent experiments. (D) Four of the patient tumor samples (T; patients 1, 2, 7 and 13 (P1, P2, P7 and P13, respectively) that demonstrated upregulation of FGFR1 as compared to their matched normal mammary tissues (N) (Additional file 7: Table S4) were further analyzed for expression of the α versus β isoforms of FGFR1. The fold increase in total FGFR1 expression as determined by real-time PCR analysis that was normalized to glyceraldehyde 3-phosphate dehydrogenase (GAP) is indicated.