However, the constitutive expression of the catalytic subunit of telomerase through agonescence and the disruption of the Rb pathway may carry a price, as the immortalized cells studied here ultimately developed specific chromosomal abnormalities (trisomy 5, trisomy 20, gain of 8q, and abnormalities of chromosome 1, some of which are seen in breast cancer and other neoplasias. The gene discussed is RB1; the disease is breast cancer.