How this instrument works
CTS5 (Clinical Treatment Score post-5-years) is a formula published by Dowsett, Sestak, Regan, and colleagues in the Journal of Clinical Oncology in 2018, built from pooled data on postmenopausal women with hormone-receptor-positive (ER+) early breast cancer enrolled in the ATAC and BIG 1-98 trials. It answers a specific, narrow question: among patients who have already finished 5 years of adjuvant endocrine therapy and remain free of recurrence at that point, what is the probability of a distant recurrence somewhere in the following 5 years — that is, between years 5 and 10 after diagnosis?
This is deliberately not a tool for a newly diagnosed patient, and not a general recurrence-risk calculator. Early recurrence risk (the first 5 years) is driven by a different mix of factors and is addressed by other tools entirely. CTS5 only applies at the 5-year, recurrence-free landmark, which is why oncologists use it specifically to help decide whether extending endocrine therapy beyond 5 years is likely to be worthwhile for a given patient.
The score is built from four clinical inputs available at that 5-year point: the number of positive lymph nodes at original diagnosis (grouped into five categories, from node-negative to more than nine positive), original tumor size in millimeters, tumor grade, and the patient's current age. These combine into a single CTS5 value, which is then sorted into three published risk bands corresponding to roughly increasing 5-to-10-year distant recurrence probability.
- Select the number of positive lymph nodes found at original diagnosis, from Negative up to More than nine positive.
- Enter tumor size in millimeters, using the original tumor's measured size.
- Select tumor grade — Grade 1 (low) through Grade 3 (high).
- Enter the patient's current age in years (this should be age now, at the 5-year post-diagnosis point, not age at diagnosis).
- Read the calculated CTS5 score and the resulting risk tier — low, intermediate, or high — for distant recurrence between years 5 and 10.
Worked example — three landmark profiles at 5 years
A patient who was node-negative at diagnosis, with a 15mm grade 1 tumor, now age 50 and recurrence-free at the 5-year mark, has a CTS5 of 0.438×0 + 0.988×(0.093×15 − 0.001×15² + 0.375×1 + 0.017×50) = 0.988×2.395 = about 2.37. That falls in the low-risk band, under 5% predicted probability of distant recurrence between years 5 and 10.
A patient with two-to-three positive nodes at diagnosis, a 30mm grade 3 tumor, now age 60 and recurrence-free at 5 years, has a CTS5 of 0.438×2 + 0.988×(0.093×30 − 0.001×30² + 0.375×3 + 0.017×60) = 0.876 + 3.98658 = about 4.86. That falls in the high-risk band, over 10% predicted probability, and is the kind of profile where extending endocrine therapy is often actively discussed.
A patient with one positive node, a 22mm grade 2 tumor, now age 55 and recurrence-free at 5 years, has a CTS5 of 0.438×1 + 0.988×(0.093×22 − 0.001×22² + 0.375×2 + 0.017×55) = 0.438 + 3.208036 = about 3.65. That sits in the intermediate band, between 5% and 10% predicted risk.
Questions
Can I use this at the time of my original breast cancer diagnosis?
No. CTS5 only applies at the 5-year, recurrence-free landmark — it estimates risk for the years 5 through 10 in patients who have already completed 5 years of adjuvant endocrine therapy without a recurrence. It was not derived to estimate risk at diagnosis or during the first 5 years, and using it at the wrong time point would give a misleading answer to a different question than the one it's built to answer.
Who is CTS5 designed for?
The model was derived from postmenopausal women with hormone-receptor-positive (ER+), early-stage breast cancer, enrolled in the ATAC and BIG 1-98 trials, who had already completed 5 years of endocrine therapy and remained recurrence-free at that point. It is not validated for hormone-receptor-negative disease, for patients who have already had a recurrence, or for use before that 5-year landmark.
What does the risk tier mean in practice?
The three bands (low under 5%, intermediate 5-10%, high over 10%) describe the published probability of distant recurrence specifically in years 5 through 10, as reported by Dowsett and colleagues. Oncologists use this alongside other clinical factors to help discuss whether extending adjuvant endocrine therapy beyond the initial 5 years is likely to provide enough additional benefit to be worthwhile for a given patient.
Why does the formula use categories for lymph nodes instead of an exact count?
The published CTS5 model groups nodal involvement into five ordinal categories (negative, one, two-to-three, four-to-nine, more than nine) rather than using the raw node count, matching how the score was derived and validated in the original 2018 study. Select the category that matches the pathology report from the original diagnosis.
Does 'age' mean age at diagnosis or age now?
Age in the CTS5 formula is age at the 5-year assessment point — that is, current age for a patient being evaluated for extended endocrine therapy after completing the initial 5 years — not age at original diagnosis.
Does a low-risk result mean recurrence is impossible?
No. The risk bands describe a probability derived from trial cohorts, not a guarantee for any individual. A low CTS5 score means a lower estimated chance of distant recurrence in years 5 through 10 based on the published model, not zero risk, and it doesn't account for every factor a treating oncologist might weigh.
Should this score decide whether I extend endocrine therapy?
No. CTS5 is a clinical reference tool meant to inform a conversation with a treating oncologist about extending adjuvant endocrine therapy past 5 years, alongside side-effect tolerance, bone health, other comorbidities, and the specific evidence for extended therapy in a given situation. It is not a standalone treatment decision.
References
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.