(Reuters) - Mersana Therapeutics said on Thursday an early stage trial testing its lead cancer drug has been put on partial hold by the U.S. Food and Drug Administration after a patient’s death was possibly linked to the treatment.

No new patients will be enrolled in the study, but the current participants will continue to receive the drug, XMT-1522, Mersana said.

The experimental treatment is being tested in patients whose advanced tumors express a protein called HER2, including those with cancers of the breast, lung and stomach.

The partial clinical hold does not affect early stage trials of Mersana’s other cancer drug, XMT-1536, which are currently underway, the company said.

Mersana’s shares were halted in premarket trade.