CTS5 Calculator: Late Breast Cancer Recurrence Risk

1. What CTS5 Is For

Open the calculator: CTS5 Late Breast Cancer Recurrence.

CTS5 is useful because the clinical question at year 5 is different from the question at diagnosis. At diagnosis, clinicians often focus on chemotherapy benefit, genomic assays, nodal burden, local therapy, and the first endocrine plan. At year 5, the discussion shifts toward residual risk, endocrine toxicity, bone health, menopausal status, competing comorbidities, and the patient's willingness to continue therapy for incremental risk reduction.

Use the CTS5 calculator as a decision-support tool, not as a directive. A low-risk result can support a conversation about stopping endocrine therapy when toxicity is meaningful. An intermediate or high-risk result can support a more detailed discussion about continuing therapy, switching endocrine agent, optimizing bone protection, or integrating genomic late-recurrence information when available.

2. Inputs and Formula

CTS5 uses four variables that are usually available from the original pathology report and treatment record:

• Age at diagnosis
• Invasive tumor size in millimeters
• Tumor grade
• Number of positive lymph nodes

The OncoToolkit implementation caps tumor size at 30 mm for the formula and maps positive lymph nodes into nodal groups: 0, 1, 2-3, 4-9, and more than 9 involved nodes. This mirrors the published clinicopathologic scoring structure and avoids overinterpreting very large raw tumor-size values outside the intended functional form.¹

3. Interpreting Risk Categories

CTS5 groups patients into late distant recurrence risk categories:

| CTS5 score | 5-10 year late distant recurrence category | | --- | --- | | Less than 3.13 | Low risk, typically under 5% | | 3.13 to 3.86 | Intermediate risk, typically 5% to 10% | | Greater than 3.86 | High risk, typically greater than 10% |

These thresholds are best read as categories for late distant recurrence risk, not as automatic endocrine therapy orders. A patient with a high CTS5 score may still reasonably stop therapy because of severe arthralgia, osteoporosis, thromboembolic risk, frailty, or personal priorities. Conversely, a patient with an intermediate score and excellent tolerance may reasonably continue if the expected benefit and harms are acceptable.

The original CTS5 work separated post-5-year distant recurrence risk in large endocrine therapy datasets, but later studies emphasize population and subtype limits. It is most commonly applied in hormone receptor-positive, HER2-negative or HER2-unselected early breast cancer. Use extra caution in HER2-positive disease, where contemporary anti-HER2 therapy and validation concerns may weaken calibration.³

4. Practical Workflow at the Five-Year Visit

1. Confirm the patient is eligible for the question. CTS5 is intended for patients with ER-positive early breast cancer who are distant recurrence-free after approximately 5 years of endocrine therapy.
2. Reconstruct the baseline pathology. Pull age at diagnosis, invasive tumor size, grade, and positive node count from the primary report before opening the calculator.
3. Calculate CTS5. Use the numeric score and category to frame residual distant recurrence risk from years 5 to 10.
4. Layer in treatment tolerance. Review vasomotor symptoms, arthralgia, sexual health, mood, adherence, bone density, fracture risk, cardiovascular risk, and competing medications.
5. Discuss options rather than a single answer. Options may include stopping endocrine therapy, continuing the current agent, switching agent class, adding bone protection, or obtaining additional prognostic information when appropriate.
6. Document the reasoning. Record the CTS5 category, the patient-specific toxicity context, and the shared decision made.

5. Related Breast Prognosis Tools

CTS5 sits in a broader breast oncology toolbox. It is often helpful to name the question before choosing the model.

For broader breast cancer calculator discovery, visit the breast cancer hub. For risk-model comparisons outside the post-treatment setting, see Gail vs Tyrer-Cuzick vs CanRisk.

6. Clinical FAQ