Paying for care
Medicare Part D vs Part B for cancer drugs
How Medicare categorizes cancer drugs between Part B and Part D, what each covers, different cost-sharing structures, and why the distinction matters for your bill.
Medicare splits drug coverage between two different programs with different rules. Part B covers drugs administered in a clinical setting. Part D covers drugs filled at a retail or specialty pharmacy. The distinction matters because cost-sharing, coverage rules, and financial-assistance options differ substantially between the two programs.
This guide explains which cancer drugs fall under each program, how cost-sharing works, and why the difference matters.
The basic rule
- Part B covers drugs that must be administered by a healthcare professional, typically injected or infused, in a physician office or hospital outpatient setting. These have HCPCS J-codes.
- Part D covers drugs the patient fills at a retail or specialty pharmacy, typically self-administered oral pills or tablets.
Cancer drugs under Part B
Common cancer drugs covered under Part B include:
- Checkpoint-inhibitor immunotherapy: Keytruda, Opdivo, Yervoy, Tecentriq
- HER2-targeted antibodies: Herceptin, Perjeta, Kadcyla, Enhertu
- VEGF and bone-targeted agents: Avastin, Xgeva
- Cytotoxic chemotherapy given by infusion (platinums, taxanes, doxorubicin, etc.)
- Radiation therapy drugs (contrast agents, adjuncts)
Part B also covers many of the pre-medications administered with infusion, anti-nausea drugs given in-office, and most drugs given through durable medical equipment.
Cost-sharing under Part B
- Part B deductible ($240 for 2024) applies once per year
- 20 percent coinsurance on most services after the deductible, with no annual out-of-pocket cap under Original Medicare
- Medigap plans typically cover the 20 percent coinsurance
- Medicare Advantage plans apply the plan’s annual out-of-pocket maximum ($8,850 in-network for 2024)
Medicare reimburses Part B drugs at Average Sales Price (ASP) plus 6 percent. ASP is published quarterly by CMS and is the foundation of Part B drug cost analysis.
Cancer drugs under Part D
Common cancer drugs covered under Part D include:
- CDK4/6 inhibitors: Ibrance, Verzenio
- EGFR-targeted oral: Tagrisso
- PARP inhibitors: Lynparza
- Androgen receptor inhibitors: Xtandi
- Oral chemotherapy (capecitabine, temozolomide)
- Oral hormonal therapy (anastrozole, letrozole, tamoxifen)
Part D is administered by private prescription drug plans under contract with Medicare. Coverage details vary by plan.
Cost-sharing under Part D
Part D uses a tiered formulary with different cost-sharing for each tier:
- Generic (low-cost copay)
- Preferred brand (moderate copay)
- Non-preferred brand (higher copay)
- Specialty (highest cost-sharing, typically coinsurance rather than copay)
Most cancer drugs land in the specialty tier. Cost-sharing can be 25 to 33 percent of the drug’s full price until the patient hits the catastrophic coverage threshold.
The Inflation Reduction Act has added substantial protections:
- 2024: Catastrophic coverage eliminates 5 percent patient coinsurance above the threshold, effectively capping out-of-pocket
- 2025: Annual Part D out-of-pocket capped at $2,000
- 2025: Option to spread annual out-of-pocket evenly across the year rather than paying front-loaded
Extra Help
Low-income Medicare beneficiaries can apply for Extra Help via SSA.gov. Extra Help reduces Part D copays to a few dollars per prescription, which transforms the affordability picture for oral cancer drugs.
Why the distinction matters
Several practical implications for cancer patients:
1. Site of care can change the program that pays
Some drugs can be administered in either an outpatient setting (Part B) or self-administered at home (Part D). The same active ingredient in different dosage forms may fall under different programs.
2. Copay assistance rules differ
Manufacturer commercial-insurance copay cards cannot be used by Medicare beneficiaries for either Part B or Part D drugs. However, manufacturer patient assistance programs (which provide drugs at no cost to income-eligible patients) are available for both.
Disease-foundation copay programs (HealthWell, PAN, CancerCare) can help with Part D drug copays for Medicare beneficiaries, within program eligibility rules.
3. Prior authorization differs
Part D plans frequently require prior authorization for specialty cancer drugs. Part B does not require prior authorization under Original Medicare for most drugs (Medicare Advantage plans often do require it).
4. Annual cost-share structure differs
Part B has the one-time annual deductible plus coinsurance. Part D has deductible, initial coverage, and now (2025) a $2,000 annual out-of-pocket cap. For patients on expensive Part D drugs, the 2025 cap is a significant improvement over prior years.
When a drug might move between programs
Occasionally a drug is available in both infused and oral forms, or its administration setting changes. Examples:
- Some anti-nausea drugs (ondansetron) are covered under Part B when administered during infusion but under Part D when filled at a retail pharmacy.
- Some targeted therapies have both IV and subcutaneous formulations. The IV formulation is typically Part B; the subcutaneous is sometimes Part D.
If your oncologist gives you a choice between formulations, the payment structure is worth discussing.