June 17 (Reuters) - Germany's BioNTech SE said in a regulatory filing on Monday the U.S. Food and Drug Administration has placed a partial clinical hold on an early-stage study of its experimental cancer drug.

The drug, an antibody-drug conjugate (ADC), was being studied in a trial sponsored by China-based MediLink, in patients with types of non-small cell lung cancer or breast cancer who have received prior forms of treatment.

ADCs, often described as "guided-missile" cancer drugs, are designed to target only cancer cells, unlike conventional chemotherapy, potentially reducing damage to normal cells.

The U.S. health regulator has shared with MediLink concerns that the drug, BNT326/YL202, may, at higher doses, expose humans to unreasonable and significant risk of illness or injuries.

The partial hold affects the enrollment of new patients in the trial in the U.S., BioNTech said.

BioNTech's COVID-19 vaccine, on which it partners with U.S. drugmaker Pfizer, was widely used during the pandemic but sales have declined in recent months.

The company is now investing money earned during the pandemic in cancer drug development. (Reporting by Sriparna Roy in Bengaluru; Editing by Krishna Chandra Eluri)