Shares of CytomX Therapeutics (CTMX -1.07%) were crashing 40.1% lower as of 11:44 a.m. ET on Tuesday. The steep decline came after the company announced disappointing preliminary results from a phase 2 study evaluating CX-2029 in treating patients with either advanced squamous non-small cell lung cancer (sqNSCLC) or head and neck squamous cell carcinoma (HNSCC). CX-2029 is an antibody-drug conjugate that's being co-developed by CytomX and AbbVie (ABBV 1.23%).
CytomX Therapeutics Chairman and CEO Sean McCarthy said in a press release that the company was "pleased" to report the preliminary results. He added that CytomX is "encouraged" by the response rates seen and the low discontinuation rate in the phase 2 study.
So why did the biotech stock plunge with this seemingly positive reaction?
McCarthy is doing what many biopharmaceutical executives do when they have disappointing news to share. Like Bing Crosby once sang, he accentuated the positive. However, the lyrics to that old song also mentioned eliminating the negative. CytomX wasn't able to do that.
The company reported an objective response rate (the percent of patients whose tumors decreased) of 18.8% in patients with advanced sqNSCLC who were treated with CX-2029. The objective response rate for patients with HNSCC was only 4%.
However, disease-control rates looked better with both types of cancer -- 87.5% for sqNSCLC and 56% for HNSCC. The safety profile for CX-2029 was also consistent with what was observed in the phase 1 study of the antibody-drug conjugate.
CytomX and AbbVie are continuing enrollment in the phase 2 study of patients with lung cancer. The partners expect to provide additional updates in 2022.