Clovis Oncology's (CLVS) lung cancer drug CO-1686 was in the spotlight at ASCO today, and, while the drug seemed to be potentially more effective than AstraZeneca's (AZN 5.38%) competitor AZD9291, the stock still dropped.

In a phase 1/2 trial, CO-1686 caused high blood sugar in 22% of patients, according to Clovis, and CEO Pat Mahaffay reportedly commented that a few patients had to receive insulin injections to handle their hyperglycemia.

In this video, from Monday's Market Checkup, the Motley Fool's health care-focused investing show, analysts Michael Douglass and David Williamson discuss the side effects and what this could mean for Clovis moving forward.