Scientists aren't far away from creating blood tests that can be used to detect the earliest stages of cancer, Guardant Health co-founder and CEO Helmy Eltoukhy said Monday.

The Silicon Valley oncology company, backed by SoftBank, is working with U.K.-based AstraZeneca to develop blood tests to help identify cancer patients likely to respond well to treatment with AstraZeneca's oncology therapies.

Bits of cancer DNA can be found in a patient's blood and give doctors clues about which treatments are most likely to work. So-called "liquid biopsy" tests, which can detect this tiny genetic material, are already nearly a standard of care for people with stage 3 or 4 cancer, a cancer that is far along in its growth, Eltoukhy said.

"We're not that far away from seeing the promise becoming a reality of a blood test for early detection," Eltoukhy told CNBC's Meg Tirrell at the 2019 American Society of Clinical Oncology meeting in Chicago.

Doctors have the ability to use tissue biopsies, tiny pieces of tumors removed surgically from patients, to determine which genes are driving cancer growth. However, tissue biopsies can sometimes be difficult to obtain, especially in patients with lung cancer.

Late last year, Eltoukhy said Guardant's product has been used in 50 different types of cancers, but lung cancer is about 45% of the volume because the traditional tissue biopsy is the most difficult and has the highest failure rate.

Guardant expects liquid biopsies to help patients where tissue biopsies cannot. A number of other companies are also working to bring blood-based cancer tests to the market, including Exact Sciences, California-based Grail and Verily-backed Freenome.

Shares of Guardant Health closed more than 1% higher Monday to $78.17 a share. The stock is up more than 142% since it began trading on the Nasdaq in October 2018.