AstraZeneca has made a preliminary approach to Gilead Sciences about a potential merger, according to Bloomberg.

AstraZeneca informally contacted Gilead last month to gauge its interest in a possible tie-up asking not to be identified because the details are private, reports Bloomberg. AstraZeneca didn’t specify terms for any transaction, they said.

No decisions have been made on how to proceed and the companies aren’t in formal talks, the people added.

A spokesman for AstraZeneca said the company doesn’t comment on “rumors or speculation, reports Bloomberg.