CMS Maintains Non-Coverage for Human Tumor Stem Cell Drug Sensitivity Assays Under NCD 253
CMS has updated NCD 253, its National Coverage Determination governing human tumor stem cell drug sensitivity assays, with a modified policy effective March 12, 2026. The update maintains the longstanding Medicare non-coverage position for these assays, which are used to expose tumor stem cell colonies to anticancer drugs and observe cytotoxic effects. For oncology billing teams and RCM directors, the key takeaway is straightforward: these assays remain classified as experimental and will not be reimbursed under Medicare.
| Field | Detail |
|---|---|
| Payer | CMS (Centers for Medicare & Medicaid Services) |
| Policy | Human Tumor Stem Cell Drug Sensitivity Assays |
| Policy Code | NCD 253 |
| Change Type | Modified |
| Effective Date | 2026-03-12 |
| Impact Level | Medium |
| Specialties Affected | Oncology, Hematology/Oncology, Clinical Laboratory, Pathology |
| Key Action | Audit any claims submitted for tumor chemosensitivity assays and ensure payer-sourced ABNs are in place before testing is ordered for Medicare beneficiaries. |
What NCD 253 Covers: CMS Policy on Tumor Drug Sensitivity Testing
The Centers for Medicare & Medicaid Services administers NCD 253 under the Diagnostic Laboratory Tests benefit category. The policy governs a specific type of chemosensitivity testing where human tumor stem cell colonies are grown in tissue culture, exposed to anticancer drugs, and monitored for cytotoxic effects.
The purpose of these assays is clinically meaningful in concept: they aim to screen potential anticancer drugs and predict how individual patients' tumors will respond, theoretically enabling more personalized chemotherapy selection. Despite that clinical rationale, CMS has consistently maintained that the evidence base does not support routine Medicare coverage.
The policy also explicitly addresses the Fluorescent Cytoprint Assay—a miniaturized organ culture system for cancer chemosensitivity testing. This assay uses low-power microscopy and a noncytotoxic fluorescence probe to provide qualitative visual estimation of cell kill. It, too, falls under the non-covered designation.
CMS Non-Coverage Determination: Why These Assays Are Considered Experimental
CMS is direct in its coverage rationale under NCD 253: human tumor drug sensitivity assays are considered experimental and are therefore not covered under Medicare at this time.
Two specific testing approaches are called out as non-covered:
| # | Excluded Procedure |
|---|---|
| 1 | Standard human tumor drug sensitivity assays — the core clonogenic assay methodology where tumor stem cells are grown and tested against anticancer agents. |
| 2 | Assays based on tumor microorgans — the clinical application of testing in tumor microorgans rather than in clones derived from single cells is independently designated as experimental and non-covered. |
The "at this time" language in the policy is worth noting. It signals that CMS has not permanently closed the door on this technology—but until a reconsideration request produces a positive coverage determination, these services will not be reimbursed for Medicare beneficiaries regardless of the clinical indication.
For billing teams, the experimental/investigational designation has significant downstream implications. Claims submitted without proper documentation of the non-coverage status—and without a valid Advance Beneficiary Notice of Noncoverage (ABN)—expose practices to recoupment risk and potential compliance issues.
| Previous Version | Current Version |
|---|---|
| Coverage is considered experimental and investigational for all indications | Coverage is considered medically necessary when specific criteria are met |
| Prior authorization is not required | Prior authorization is required for initial treatment |
| Documentation must include clinical history | Documentation must include clinical history |
| Re-review every 24 months | Re-review every 12 months with updated clinical documentation |
Affected Codes
The policy document for NCD 253 does not list specific CPT or HCPCS codes associated with this coverage determination. There are no ICD-10-CM diagnosis codes specified in the policy data.
This is not uncommon for older NCDs that predate the modern code-specific coverage framework. The absence of assigned codes means billing teams cannot rely on a clean code-level denial pattern to catch these claims automatically—making manual review and order-level controls more important.
Covered Codes
No codes are covered under this policy. CMS has designated all applicable human tumor stem cell drug sensitivity assay services as non-covered experimental procedures.
Non-Covered / Experimental Services
| Service Description | Coverage Status | Reason |
|---|---|---|
| Human tumor drug sensitivity assays (clonogenic method) | Not Covered | Experimental per NCD 253 |
| Assays based on tumor microorgan testing | Not Covered | Experimental per NCD 253 |
| Fluorescent Cytoprint Assay | Not Covered | Experimental per NCD 253 |
Note: Because NCD 253 does not list specific CPT or HCPCS codes, practices should work with their clinical laboratory partners to identify any internal codes or test identifiers used for chemosensitivity assays and flag those for pre-claim review.
What Your Billing Team Should Do
The March 12, 2026 effective date gives billing teams a defined window to audit workflows and tighten controls. Here are the specific actions to prioritize:
| # | Action Item |
|---|---|
| 1 | Audit orders and pending claims immediately. Pull any claims submitted or in queue for tumor chemosensitivity assays billed to Medicare. Identify whether any have been submitted without ABN documentation. If you find submitted claims with no ABN, escalate to your compliance officer before the effective date. |
| 2 | Issue an ABN before testing is ordered for Medicare beneficiaries. Because NCD 253 classifies these assays as experimental, a properly executed Advance Beneficiary Notice of Noncoverage is required when a Medicare patient may want to proceed at their own expense. The ABN must be signed before the service is rendered—not retroactively. |
| 3 | Contact your clinical laboratory and reference lab partners. If your practice orders these assays and sends specimens to a reference lab, confirm that your lab partner is aware of the NCD 253 non-coverage status and is not billing Medicare directly for these services. Downstream billing errors can still create compliance exposure for the ordering provider. |
| 4 | Flag this in your EHR or order entry system. Because there are no specific CPT/HCPCS codes listed in the policy, automated claim edits won't catch these services by code alone. Work with your IT or EHR team to add an alert at the order level when a chemosensitivity assay is ordered for a Medicare patient. |
| 5 | Review your payer mix for commercial coverage differences. NCD 253 governs Medicare only. Commercial payers may have different—and in some cases more permissive—coverage policies for chemosensitivity testing. Verify coverage separately for each commercial payer before assuming non-coverage applies universally. |
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