Oncotype DX: Gene Test for Breast Cancer

What is Oncotype DX?

Oncotype DX is a genomic assay that analyzes 21 genes from surgically removed breast cancer tissue. It is especially useful in early-stage breast cancer (Luminal A and Luminal B, ER+, HER2–, LN–) patients to determine whether adjuvant chemotherapy is necessary after surgery.

Eligible patient groups include Luminal A and Luminal B breast cancers that have the following characteristics:

Hormone receptor positive (ER+)
HER2-negative
No spread to the axillary lymph nodes (LN–)

This test is done by analyzing a 21-gene assay on surgically removed tumor tissue to calculate a Recurrence Score (RS), which is used to indicate the risk of recurrence and the likelihood of benefiting from chemotherapy.

Interpreting the Recurrence Score (RS)

Oncotype DX results are scored from 0–100, with interpretations based on data from the TAILORx trial (NEJM 2018).

RS 0–10 Low risk

Endocrine therapy alone is sufficient; chemotherapy is unnecessary.

RS 11–25 Intermediate risk

Women ≥50 years: Chemotherapy offers little to no benefit → Endocrine therapy alone.
Women <50 years: If RS is close to 21–25, chemotherapy may offer some benefit → requires individualized assessment.

RS ≥26 High risk

Chemotherapy combined with endocrine therapy is recommended.

Supporting Evidence: TAILORx Trial

Population: ER+, HER2–, LN– breast cancer patients.

Intervention: Endocrine therapy alone vs. endocrine therapy + chemotherapy.

Results:

RS 11–25 (women ≥50 years): Chemotherapy did not improve survival outcomes.
RS ≥26: Chemotherapy significantly reduced recurrence.

Benefits for Patients Who Wish to Avoid Chemotherapy

Helps make more accurate treatment decisions and reduces uncertainty in choosing chemotherapy.
Reduces unnecessary side effects (hair loss, nausea, infertility).
Provides reassurance if endocrine therapy alone is sufficient.
Prevents overtreatment and improves quality of life.

Limitations of Oncotype DX

Applicable mainly to ER+, HER2–, LN– cases.
High cost (approximately 120,000–150,000 THB in Thailand) and not covered by universal healthcare or social security schemes.
Not suitable for Triple Negative or HER2+ breast cancer.

Who is suitable for Oncotype DX testing?

Patients with early stage breast cancer (Stage I–II)
The tumor is ≤ 5 centimeters in size.
No or only minor lymph node metastasis.
The cancer is ER+/PR+ and HER2–.

Oncotype DX is a gene test that helps patients and their doctors tailor treatment options for early-stage breast cancer, reducing the risk of unnecessary chemotherapy and increasing confidence in treatment.

Despite its high cost and lack of government coverage, Oncotype DX is an important tool. Especially in patients who do not want to receive chemotherapy, if you or someone close to you is in a high-risk group, you should consult an oncologist to determine the appropriateness of this test.