TL;DR: The Centers for Medicare & Medicaid Services modified NCD 253, the national coverage determination governing human tumor stem cell drug sensitivity assays, effective January 9, 2026. Medicare does not cover these assays. Here's what that means for your billing team.
This update to the CMS human tumor stem cell drug sensitivity assay coverage policy confirms the non-coverage position CMS has held for years. NCD 253 in the CMS Medicare system classifies both human tumor drug sensitivity assays and the Fluorescent Cytoprint Assay as experimental. No specific CPT or HCPCS codes are listed in the policy. If your oncology or lab billing team submits claims for these assays to Medicare, expect a claim denial.
| Field | Detail |
|---|---|
| Payer | Centers for Medicare & Medicaid Services (CMS) |
| Policy | Human Tumor Stem Cell Drug Sensitivity Assays |
| Policy Code | NCD 253 |
| Change Type | Modified |
| Effective Date | 2026-01-09 |
| Impact Level | Medium — high denial risk for oncology labs billing these assays to Medicare |
| Specialties Affected | Oncology, clinical laboratory, hematology/oncology |
| Key Action | Audit your charge capture and LCD review process before submitting any chemosensitivity assay claims to Medicare |
CMS Human Tumor Stem Cell Drug Sensitivity Assay Coverage Criteria and Medical Necessity Requirements 2026
NCD 253 is the National Coverage Determination governing whether Medicare covers human tumor stem cell drug sensitivity assays. The short answer: it does not.
CMS defines these assays as procedures that expose human tumor stem cell colonies — grown in tissue culture — to anticancer drugs. The purpose is to observe cytotoxic effects, screen potential anticancer drugs, and predict how a specific patient's tumor will respond to treatment. In theory, that helps oncologists select the most effective drug for a given patient.
That clinical rationale sounds compelling. CMS disagrees with it — at least for now. The agency classifies these assays as experimental under the Medicare benefit category for diagnostic laboratory tests.
The coverage policy also addresses the Fluorescent Cytoprint Assay specifically. This is a miniaturized organ culture system for cancer chemosensitivity testing. It uses low-power microscopy and a noncytotoxic fluorescence probe to estimate cell kill qualitatively. CMS treats it the same way: experimental, not covered.
The word "experimental" in NCD language is not soft. It's a hard non-coverage determination. You won't satisfy medical necessity requirements for Medicare reimbursement on these assays, regardless of how well-documented the clinical indication is in the patient record.
No prior authorization process exists here because prior authorization is only relevant when coverage is possible. CMS has closed the door before prior auth even becomes a question.
CMS Human Tumor Stem Cell Drug Sensitivity Assay Exclusions and Non-Covered Indications
The entire scope of NCD 253 is non-coverage. There are no covered indications in this policy. That's worth saying plainly because some NCD policies have partial coverage — a covered indication alongside a non-covered one. NCD 253 is not that.
Two distinct assay types fall under this non-coverage determination:
Human tumor drug sensitivity assays (cell clone-based). These assays derive test colonies from single cells — clones. CMS considers the clinical application of this approach experimental. The biology may be sound. The clinical evidence for guiding individual treatment decisions has not met the Medicare coverage bar.
The Fluorescent Cytoprint Assay (tumor microorgan-based). This assay tests tumor microorgans — not clones derived from single cells. CMS notes that distinction explicitly and still reaches the same conclusion: experimental, not covered.
The real issue here is that CMS draws the non-coverage line at clinical application, not at the underlying science. These assays may have valid research uses. Using them to guide individual patient drug selection for a Medicare patient — and billing Medicare for that — is what triggers the denial.
If your laboratory performs these assays as part of a covered clinical trial, the billing pathway may differ. CMS has separate coverage provisions for routine costs associated with qualifying clinical trials. That's a distinct policy and a distinct billing analysis. Talk to your compliance officer before billing Medicare for any chemosensitivity assay, even in a research context.
Coverage Indications at a Glance
| Indication | Status | Relevant Codes | Notes |
|---|---|---|---|
| Human tumor drug sensitivity assay — clone-based (single cell derived) | Not Covered — Experimental | Not listed in policy | CMS considers clinical application experimental; no reimbursement available under Medicare |
| Fluorescent Cytoprint Assay — tumor microorgan-based chemosensitivity testing | Not Covered — Experimental | Not listed in policy | Applies to qualitative cell kill estimation via low-power microscopy and fluorescence probe |
| Cancer chemosensitivity testing generally under NCD 253 | Not Covered — Experimental | Not listed in policy | Entire NCD is a non-coverage determination; no partial coverage exceptions listed |
CMS Human Tumor Stem Cell Drug Sensitivity Assay Billing Guidelines and Action Items 2026
This policy took effect January 9, 2026. If your team has been billing — or considering billing — these assays to Medicare, act now.
| # | Action Item |
|---|---|
| 1 | Audit your charge capture immediately. Pull any claims submitted on or after January 9, 2026 that relate to chemosensitivity testing, tumor drug sensitivity assays, or fluorescent cytoprint testing. If those claims went to Medicare, review them for denial exposure. Human tumor stem cell drug sensitivity assay billing to Medicare is not reimbursable under NCD 253. |
| 2 | Check your lab's HCPCS code usage. The NCD 253 policy does not list specific CPT or HCPCS codes. That gap creates a real billing risk. Without assigned codes in the NCD itself, your coders may have submitted claims using unlisted lab codes, miscellaneous chemistry codes, or molecular pathology codes without realizing CMS's non-coverage position applies. Identify every code your lab has used to bill these services and cross-reference each one against NCD 253. |
| 3 | Review any ABN (Advance Beneficiary Notice of Noncoverage) workflows. Because NCD 253 is a hard non-coverage determination, Medicare patients who want these assays and will pay out of pocket must receive a properly executed ABN before the service. If your team isn't issuing ABNs for these assays today, fix that before the next order comes in. Billing guidelines for non-covered services require this. |
| 4 | Check your Medicare Administrative Contractor (MAC) for any local coverage determinations. NCD 253 sets national policy. But your MAC may have issued a local coverage determination (LCD) that addresses chemosensitivity testing or adjacent laboratory services. An LCD could clarify which codes your MAC will process — even if only to formally deny them. Know what your MAC says before your next claim goes out. |
| 5 | Do not assume a clinical trial exemption applies automatically. If your oncology team performs these assays under an IRB-approved protocol, the routine-cost-in-clinical-trial rule may open a narrow billing pathway. But it requires the trial to meet CMS's qualifying criteria, and the claim must be coded correctly to reflect the trial context. This is not a default workaround. Loop in your compliance officer before billing Medicare for any assay under NCD 253, even in a research setting. |
| 6 | Educate your oncology billing team on the "experimental" designation. Revenue cycle staff sometimes see "experimental" and assume there's a prior authorization path that could unlock coverage. There isn't — not here. NCD 253 has no coverage track, no exception criteria, and no medical necessity documentation pathway that changes the outcome. The denial is the policy. |
| 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 |
CPT, HCPCS, and ICD-10 Codes for Human Tumor Stem Cell Drug Sensitivity Assays Under NCD 253
NCD 253 does not list specific CPT codes, HCPCS codes, or ICD-10-CM diagnosis codes. CMS published this coverage policy without assigned billing codes.
That's not unusual for older NCDs — many predate the era of code-level specificity in coverage documents. But it creates a real operational problem for your billing team.
What the Absence of Codes Means for Your Team
Without a code list in the NCD itself, there's no automatic claims-edit trigger that will catch these claims before they go out. Your team needs to know the policy exists and apply it manually. The denial risk is real even without a code-level block.
Contact your MAC directly. Ask whether they have issued an LCD or billing article that maps specific codes to NCD 253. Some MACs have done this work. If yours has, get that list and build it into your charge capture logic.
No Fabricated Codes
This post will not invent codes that don't appear in the policy data. Human tumor stem cell drug sensitivity assay billing has no confirmed code list from CMS at this time. Any code a coder might use — whether an unlisted procedure code, a chemistry panel code, or a molecular pathology code — would require separate validation against your MAC's billing articles and CMS claims processing instructions.
If your lab has been billing these services under any code, that code deserves a compliance review against NCD 253 before the next claim submits.
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