Shares of Revolution Medicines (RVMD 2.97%) were crashing 42.5% lower as of 11:13 a.m. ET on Monday. The steep decline came after the oncology company presented results on Sunday for RMC-6236 from a phase 1 study targeting the treatment of non-small cell lung cancer (NSCLC) and pancreatic ductal adenocarcinoma (PDAC) at the European Society for Medical Oncology (ESMO) Congress held in Madrid, Spain.

Why Revolution Medicines' data disappointed

Expectations appeared to be high for Revolution Medicines and for RMC-6236 going into ESMO, as evidenced by the biotech stock soaring to more than 40% year to date last week. However, the data for RMC-6236 didn't meet those expectations.  

Revolution reported that 37.5% of patients with NSCLC responded to treatment with RMC-6236. However, three of the 14 partial responses were unconfirmed. With those unconfirmed responses excluded, the objective response rate was only 30%.

The story was even less impressive for RMC-6236 in treating PDAC. Nine of 46 patients (19.6%) achieved a partial response. However, four of those partial responses were unconfirmed.

Revolution Medicines CEO Mark Goldsmith said in a press release that the data supported the view that "RMC-6236 can lead to meaningful clinical responses in patients at dose levels that are generally well tolerated." Leerink Partners analyst Jonathan Chang agreed in a report written after the presentation. However, Chang acknowledged that the results for Revolution's experimental drug "may be below investor expectations." 

Is Revolution Medicines stock a buy on the sell-off?

RMC-6236 could still prove to be an effective cancer therapy both on its own and as part of potential combinations. It's possible that Revolution Medicines' shares could rebound as investors move past their initial disappointment about the phase 1 data.

However, the stock is likely to remain highly volatile. Risk-averse investors will be better off looking elsewhere.