CA 15-3 (Cancer Antigen 15-3)

Pick Ordered or Not ordered to see the note.

Indicated when

• —Serial monitoring of response to systemic therapy in a patient with known metastatic breast cancer, under the direction of the treating oncologist, alongside imaging and clinical assessment, not as a stand-alone result [3]

Not indicated when

• —Routine surveillance for recurrence in a patient previously treated for early-stage or localized breast cancer with no evidence of current disease [1, 2]
• —Screening for breast cancer, or investigating a new breast lump, in a patient with no personal history of breast cancer
• —General 'wellness' or tumour-marker panel with no personal history of breast cancer

Why not

ASCO's 2026 breast cancer follow-up guideline update again discourages routine blood work, including CEA, CA 15-3, and CA 27.29, for asymptomatic patients after primary treatment: no evidence shows these tests catch recurrence earlier than clinical symptoms would, or that catching it earlier this way improves survival, while they reliably add false-positive results, follow-up testing, and anxiety ([2], summarizing [1]). This restates a position ASCO has held since its 2006 and 2013 updates. Choosing Wisely's oncology position is the same in principle: don't order tests to detect recurrence in asymptomatic patients without a realistic expectation that earlier detection improves survival [4].

Better first step

For a patient previously treated for breast cancer with no new symptoms, follow the guideline-recommended follow-up plan of history, physical exam, and mammography, and investigate any new symptom or exam finding directly rather than adding CA 15-3. For a patient with no personal history of breast cancer who has a breast concern, use clinical breast exam and standard breast imaging (mammography/ultrasound) rather than a tumour marker.

Typical ND rationale

An ND may include CA 15-3 in a general tumour-marker or cancer-screening panel, reasoning that it is a well-known breast-cancer-associated marker and that checking it, particularly in someone with a family history or a prior breast cancer diagnosis, offers early warning or reassurance.

Ontario coverage & CONO orderability

OHIP status

uninsured

CA 15-3 is not listed by name in the 2026 Schedule of Benefits for Laboratory Services [5]. A LifeLabs non-OHIP-billable test list republished by an Ontario hospital laboratory (effective June 2025) confirms 'CA 15.3' as a patient-paid, non-OHIP test in Ontario, used here as the secondary evidence the coverage rules call for [6]. ND-ordered testing is patient-paid regardless [7, 8]. (Secondary evidence: a community-lab price list, not a ministry statement. Hospital-lab funding for oncology follow-up is separate and was not checked.)

CONO orderable

Yes — CONO list #33

CONO list item 33, blood: 'CA15-3.'

Linked conditions

• Tumour markers to check for 'hidden' cancer ↗

Counselling script

“CA 15-3 isn't used to screen for breast cancer or to watch for it coming back after treatment, because studies haven't shown it catches recurrence earlier than a regular checkup would, or that it changes outcomes; mainly it adds false alarms. It does have a role for people already being treated for metastatic breast cancer, but that's an oncology-team decision alongside scans. If you have a breast lump or new symptom, let's start with an exam and imaging instead.”

Revisit if

• —A new breast lump, skin or nipple change, or other symptom suspicious for breast cancer develops
• —A diagnosis of metastatic breast cancer is made and the oncology team requests marker monitoring

References

1. [1]American Society of Clinical Oncology (2026). Breast Cancer Follow-Up and Surveillance After Primary Treatment: ASCO Guideline Update. link2026 ASCO breast cancer follow-up guideline update addresses blood-based biomarker use in surveillance
2. [2]CancerNetwork (MJH Life Sciences) (2026). Top 9 Takeaways From ASCO's 2026 Breast Cancer Surveillance Update. linkCA 15-3, CEA, and CA 27.29 remain discouraged for asymptomatic surveillance; no evidence they detect recurrence earlier or improve survival, and they add false positives and anxiety
3. [3]American Society of Clinical Oncology (2007). American Society of Clinical Oncology 2007 Update of Recommendations for the Use of Tumor Markers in Breast Cancer. linkolder guidelineHistoric ASCO recognition of some clinical utility for CA 15-3, chiefly in monitoring response to therapy, with not all applications supported
4. [4]Canadian medical oncology societies / Choosing Wisely Canada (2025). Oncology recommendations. linkDon't order recurrence-detection tests in asymptomatic patients without a realistic expectation of survival benefit
5. [5]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkCA 15-3 is not listed by name in the 2026 OHIP Schedule of Benefits for Laboratory Services
6. [6]LifeLabs (republished by Norfolk General Hospital laboratory) (2025). LifeLabs Non-OHIP Billable Test List (republished by Norfolk General Hospital laboratory, effective 2025). linkCA 15.3 appears on a LifeLabs Ontario non-OHIP-billable test list, i.e., patient-paid
7. [7]Government of Ontario (e-Laws) (2026). Health Insurance Act, R.R.O. 1990, Reg. 552: General, s. 22 (insured laboratory services). linkA lab test is insured only when ordered by a physician, midwife, or NP who has clinically assessed the patient
8. [8]Ontario Ministry of Health (2026). Ontario Health Insurance Plan: Schedule of Benefits for Laboratory Services (effective April 1, 2026). linkTests ordered by anyone other than an authorized provider, including NDs, are not insured services