Nov 30 (Reuters) - Pfizer Inc said on Wednesday its experimental biosimilar of Roche Holding AG's blockbuster breast cancer treatment Herceptin met the main goal in a key study.

Pfizer tested the safety and effectiveness of the drug, PF-05280014, in combination with chemotherapeutic agent paclitaxel against Herceptin and paclitaxel in previously untreated patients with HER2-positive metastatic breast cancer.

Biotech drugs such as Herceptin are made in living cells, and then extracted and purified. They are more complex than traditional drugs and cannot be copied with precision. Their knock-off versions are called biosimilars and not generics.

Several companies are developing biosimilar versions of top-selling biotech medicines.

The allure of biosimilars is clear, with insurers counting on the steep discounts. U.S. pharmacy benefit managers are already trimming brand-name drugs from their rosters.

(Reporting by Natalie Grover in Bengaluru; Editing by Saumyadeb Chakrabarty)