IGF1 and breast cancer: Puromycin, an old antibiotic derived from Streptomyces alboniger as a structural analog of tyrosyl tRN 1 [1], is known to induce apoptosis in breast cancer cells by insulin-like growth factor 1 (IGF-I) and exert antitumor activity in MDA-MB-231 cells via the suppression of 45S pre-ribosomal RNA and upstream binding factor (UBF) [2,3], since it terminates the ribosomal protein synthesis process by causing the premature release of a polypeptide from the ribosome in malignant cells compared to normal cells [4].