How Medigap Covers Cancer Compared to Medicare Advantage

Medigap plans work alongside Original Medicare to cover the cost-sharing that Medicare leaves behind. For cancer patients, this means Medigap covers the 20% Part B coinsurance on chemotherapy, radiation therapy, oncologist visits, imaging scans, and other outpatient cancer services. With Plan G, your maximum annual out-of-pocket cost for Part B services is just the $257 deductible in 2026.

The financial protection Medigap provides becomes clear when you consider the cost of cancer treatment. A year of chemotherapy can easily exceed $100,000 in Medicare-approved charges. Under Original Medicare alone, you would owe 20% of that amount ($20,000+) with no cap. With Medigap Plan G, you pay $257 for the year regardless of how many treatments, scans, or specialist visits you need.

Medigap also covers the Part A deductible ($1,676 per benefit period in 2026) for hospital stays, skilled nursing facility coinsurance, and Part B excess charges. This means cancer-related hospitalizations for surgery, inpatient chemotherapy, or complications are covered with no additional cost-sharing beyond your monthly premium.

Critically, Medigap plans have no network restrictions. You can see any oncologist, visit any cancer center, and participate in clinical trials at any facility that accepts Medicare. There are no referral requirements and no prior authorization for any Medicare-covered service. Your treatment decisions remain between you and your doctor without insurance company interference.

Medicare Advantage plans provide an out-of-pocket maximum (MOOP) that Original Medicare alone does not offer. In 2026, the federal MOOP cap is $9,250 for in-network services. Once you reach this amount, the plan pays 100% of covered services for the rest of the year. For cancer patients, this cap provides a ceiling on costs, but reaching it means paying thousands before full coverage begins.

The primary concern with Medicare Advantage for cancer patients is prior authorization. MA plans require prior authorization for imaging tests, radiation therapy, inpatient hospital stays, outpatient oncology services, and many chemotherapy drugs. In 2024, Medicare Advantage insurers processed nearly 53 million prior authorization requests, which was 84 times more than Original Medicare. Of those, 4.1 million were fully or partially denied. According to the AMA, 93% of physicians report care delays linked to prior authorization, and 82% say patients sometimes abandon recommended treatment due to authorization barriers.

Network restrictions present another challenge. One in five Medicare Advantage plans do not include an academic medical center in their network, and in areas with top cancer centers, two out of five plans exclude them. HMO plans require you to stay in-network (except emergencies), while PPO plans allow out-of-network care at significantly higher cost-sharing. If your oncologist or preferred cancer center is not in your plan's network, you may need to switch doctors mid-treatment or pay substantially more.

In 2026, several major hospital systems and cancer centers have stopped accepting certain Medicare Advantage plans due to reimbursement disputes and prior authorization burdens. This trend means that even if a cancer center was in your network when you enrolled, it may not remain in-network throughout your treatment. People enrolled in Original Medicare had access to more than twice as many doctors as those in Medicare Advantage, according to KFF research.

Consider a Medicare beneficiary diagnosed with breast cancer who needs surgery, 6 months of chemotherapy, radiation therapy, and ongoing monitoring. The total Medicare-approved charges for this treatment year might reach $150,000. Here is how costs compare across coverage options.

With Medigap Plan G (assuming $200/month premium): You pay the $257 Part B deductible plus $2,400 in annual premiums for a total of $2,657. Every chemotherapy session, radiation treatment, CT scan, MRI, oncologist visit, and hospital stay is covered at 100% after that $257 deductible. Your cost is the same whether treatment costs $50,000 or $500,000.

With Medicare Advantage (assuming $0 monthly premium): You pay copays and coinsurance for each service until reaching the MOOP. With $150,000 in treatment, you will almost certainly hit the $9,250 cap within the first 2-3 months. Your total annual cost is approximately $9,250 plus any out-of-network charges if you need care outside your plan's network.

With Original Medicare alone (no supplement): You pay 20% of all Part B services with no annual cap. On $150,000 in outpatient treatment, your coinsurance would be approximately $30,000. Add the Part A deductible ($1,676) for any hospital stays, and total costs could exceed $31,676 with no ceiling. This is why experts strongly recommend either Medigap or Medicare Advantage rather than Original Medicare alone for cancer patients.

One of the most important considerations for cancer coverage is that switching from Medicare Advantage to Medigap after a diagnosis can be difficult or impossible in most states. Private insurers that sell Medigap policies can use medical underwriting (reviewing your health history) to deny coverage or charge higher premiums if you apply outside of your guaranteed issue period. A cancer diagnosis would likely result in denial or significantly higher premiums.

Your guaranteed issue period for Medigap occurs when you first enroll in Medicare Part B at age 65 (or during the first 12 months of Part B if under 65 on disability). During this window, no insurer can deny you coverage or charge more based on health conditions. This is why many Medicare experts recommend enrolling in Medigap Plan G from the start, before any health issues arise.

There are limited exceptions. If you enrolled in Medicare Advantage and want to switch back to Original Medicare plus Medigap within your first 12 months on the MA plan, you have a trial right that guarantees Medigap acceptance. Additionally, some states (New York, Connecticut, Massachusetts, Maine, and Washington) require continuous open enrollment for Medigap, meaning you can switch at any time regardless of health status.

If you are currently on Medicare Advantage and have been diagnosed with cancer, you can switch to Original Medicare during the Medicare Advantage Open Enrollment Period (January 1 through March 31) or the Annual Enrollment Period (October 15 through December 7). However, obtaining a Medigap policy to go with it may require medical underwriting unless you qualify for a guaranteed issue right or live in a continuous open enrollment state.