Timely Access to Cancer Treatment Act of 2021 or the TACT Act of 2021 This bill requires insurance plans to authorize, and pharmacies contracted with the plans to dispense, anti-cancer oral medications within certain time frames. Specifically, within 24 hours after receiving a prescription, a pharmacy must inform the health care provider and plan enrollee whether it will dispense the medication. If the pharmacy will dispense the medication, it must do so within 72 hours after receiving the prescription. If the pharmacy is unable to dispense the medication, it must notify in writing the prescribing health care provider, the insurance plan, and the plan enrollee. A plan that requires prior authorization for anti-cancer oral medication must make that determination within 72 hours after receiving the request for authorization. Further, if a pharmacy provides notification that it is unable to dispense the medication, the health insurance plan must allow the enrollee to select a different pharmacy to dispense the medication, even if that pharmacy does not have a contract with the plan. In such a case, the plan may not require additional prior authorization or cost sharing. The Government Accountability Office must evaluate and report on the implementation of these requirements.