The two companies have signed a new master collaboration agreement under which HTG will develop custom assays for use in earlier stages of Merck's drug development process.
The tests were developed as part of a partnership with Merck KGaA, one of the manufacturers of the anti-EGFR therapy Erbitux.
Guardant is providing its Guardant 360 CDx test for a clinical trial of Merck's small molecule, c-Met kinase inhibitor called tepotinib.
The agreement now includes distribution of Roche's Kapa Biosystems portfolio in all geographies except the US, Brazil, and Japan.
The companies will initially focus on developing a companion diagnostic for Merck's investigational B cell lymphoma drug M7583.