Vectibix, a cancer drug made by Amgen (AMGN), did not show statistically significant survival rates for patients in a study of its effectiveness against advanced colorectal cancer.

However, certain patients lacking a specific gene that took Vectibix showed an increased survival of four months. Although these results were statistically insignificant, they may be enough to boost sales of the drug.

Amgen said in a statement that it is "encouraged" by the increase in overall survival of patients lacking a mutation in the KRAS gene. The KRAS gene occurs in approximately 40% of colon cancer patients.

Vectibix’s main competitor in the space is Erbitux, which is sold by Eli Lilly (LLY) and Bristol-Myers Squibb (BMY). Last year, Erbitux sales rose 8% to $739 million, while Vectibix sales dropped 36% to $108 million.

Shares of Amgen rose 3.5% to $54.05 on Thursday.