Chemical Pathology


Cancer antigen 15.3 (CA 15-3) should only be used to determine response to therapy in patients with metastatic breast cancer or for the early detection of recurrence in patients with previously treated stage II and stage III breast cancer. Requests should therefore only be made as advised by the specialist secondary care team.

CA 15-3 has been reported to be elevated in other malignancies and in various non-malignant conditions but should only be used as specified.

A significant proportion (25-30%) of patients with advanced breast cancer have tumours which do not produce CA 15-3.

Sample requirements

If patient on high dose biotin therapy (>5mg/day) collect sample at least 8 hours after the last dose.

For adults, 5 ml of blood taken into a narrow gold top tube (or rust top for the Acute Unit)

5ml gold tube


Send at ambient temperature to the laboratory. If unavoidable, samples can be stored refrigerated overnight.

Required information

Relevant clinical details, including site of primary tumour. Is the test being used for baseline prior to treatment or for follow-up?

Turnaround times

The assays are run once a week.
The in-lab turnaround time is less than 8 days

Reference ranges

Assayed using the Cobas CA15-3 II ECLIA

Reference range: less than 28 kU/L

This reference range was obtained by the manufacturer using a panel of samples from 378 apparently healthy non-pregnant females and gives the 97.5 percentile (%).

Half-life of CA 15-3 is 10 days following surgical removal of the primary tumour; 30 days following chemotherapy or radiotherapy.

Median doubling time is 30 days.

Further information

Lab Tests Online: CA 15-3 Test

BMJ 2009; 339: b3527 Serum tumour markers: how to order and interpret them

Page last updated 20/09/2017