The present invention provides, inter alia, methods, pharmaceutical compositions, and kits for treating or ameliorating the effects of a cancer in a subject, which cancer is refractory or resistant to non-ERK MAPK pathway inhibitor therapy. Also provided are methods for identifying a subject having cancer who would benefit from therapy with an ERK inhibitor and methods for inhibiting phosphorylation of RSK in a cancer cell that is refractory or resistant to a non-ERK MAPK pathway inhibitor.
