Switzerland's Roche Holding will help develop diagnostic tests for Merck & Co's portfolio of experimental cancer medicines under a collaboration announced by the two drugmakers on Tuesday.

Under the collaboration, for which financial terms were not disclosed, Roche Diagnostics will provide assays for use in clinical oncology programs being conducted by Merck.

Merck will also expand use of Roche's AmpliChip p53 assay to identify patients suitable for inclusion in trials.

"Effective use of companion diagnostics is an important component of our oncology development strategy focused on targeted therapies," Gary Gilliland, Merck's head of oncology research, said in a statement.

The partnership - announced as the American Society of Clinical Oncology meeting winds down in Chicago - deepens the relationship between Merck and Roche, which recently announced a co-promotion arrangement over hepatitis C medicines. Roche also announced a partnership last week with Bristol-Myers Squibb to evaluate their respective cancer drugs as a potential combination therapy for metastatic melanoma.