Final answer:
Efflux pumps are ABC-type ATPases that transport antitumor drugs out of tumor cells, inhibiting their effectiveness.
Step-by-step explanation:
The ABC-type ATPases that inhibit the effectiveness of antitumor drugs by transporting the drugs out of tumor cells are known as efflux pumps. These pumps actively pump the drugs out of the cell, preventing their accumulation to a level that would be effective against the tumor cells.