Analysis of these small-cell-transformed tumors revealed loss of RB1, a hallmark of small cell lung cancer.62, 63 Loss of RB1 may be the alteration that induces this non-small-cell to small-cell transformation, resulting in a molecular switch from dependence on the original driver oncogene to a different survival program regulated by RB1 loss.64 Here, RB1 is linked to small cell lung carcinoma.