Tyrer-Cuzick / IBIS Breast Cancer Risk Calculator
Understand how Tyrer-Cuzick/IBIS differs from Gail/BCRAT and when it supports screening or genetics discussions.
1. What Tyrer-Cuzick / IBIS Is For
The IBIS, or Tyrer-Cuzick, model estimates a woman's probability of developing breast cancer over defined time horizons, commonly 10-year and lifetime risk. It is used in high-risk breast clinics, imaging programs, and genetics triage because it incorporates a broader risk-factor profile than Gail/BCRAT.
Official/reference implementations include the IBIS Risk Assessment Tool and licensed clinical risk platforms. OncoToolkit provides this guide for clinical context and internal navigation; it does not reproduce a licensed IBIS implementation.
2. Key Inputs in the Tyrer-Cuzick Model
The exact input set depends on the implementation and version. In practical clinical use, Tyrer-Cuzick commonly draws from these domains:
| Input domain | Examples | Clinic note tip |
|---|---|---|
| Demographics | Age, height, weight, menopausal status. | Use current values and document whether menopause is natural, surgical, or treatment-related when relevant. |
| Reproductive and hormonal history | Age at menarche, age at first birth, parity, menopause, hormone therapy exposure. | Clarify nulliparity and hormone therapy duration because small entry differences may affect risk. |
| Benign breast disease | Prior biopsy, atypical hyperplasia, LCIS depending on implementation. | Use pathology reports rather than patient recollection when possible. |
| Family history | Affected relatives, lineage, age at diagnosis, ovarian cancer, bilateral breast cancer. | Separate maternal and paternal relatives and update the estimate as family history changes. |
| Breast density | BI-RADS density or other density measures depending on the platform. | Document the density source and date of mammogram used for the estimate. |
| Genetic context | Known pathogenic variants or genetic testing history, when supported. | For complex hereditary patterns, consider CanRisk/BOADICEA or genetics referral. |
3. Interpretation Workflow
- Confirm why the estimate is needed. Common uses include MRI eligibility, high-risk clinic referral, risk-reduction counseling, and genetics triage.
- Use the version requested by the workflow. Imaging centers and health systems may specify IBIS/Tyrer-Cuzick v8 or a licensed platform implementation.
- Enter breast density consistently. Adding density can materially change risk estimates; document whether it was included.
- Check for hereditary red flags. Young-onset breast cancer, ovarian cancer, male breast cancer, pancreatic cancer, metastatic prostate cancer, or known familial variants may require genetics-specific assessment rather than a screening-risk-only calculation.
- Map the output to policy, not instinct. Many screening protocols use lifetime risk thresholds for supplemental MRI, but exact criteria vary by country, guideline, payer, and institution.
Clinical caution: A lifetime risk estimate is not the same as a diagnosis, and it is not a standalone mandate for MRI, chemoprevention, genetic testing, or surgery. Use the estimate to support a documented, patient-centered decision.
4. Tyrer-Cuzick Compared With Gail and CanRisk
| Question | Best fit | Why | OncoToolkit link |
|---|---|---|---|
| 5-year invasive breast cancer risk for prevention-medication discussion | Gail / BCRAT | Compact, widely recognized, and aligned with many chemoprevention thresholds. | Gail calculator |
| Lifetime risk for screening-risk triage with density and family history | Tyrer-Cuzick / IBIS | Richer than Gail and commonly used by breast imaging/high-risk screening programs. | This guide |
| Carrier probability and combined breast/ovarian genetics-oriented risk | CanRisk / BOADICEA | Designed for detailed pedigree, genetic testing, PRS, ovarian risk, and carrier probability. | CanRisk guide |
For a side-by-side overview, see Gail vs Tyrer-Cuzick vs CanRisk Breast Risk Models.
5. Common Pitfalls and Limitations
Breast density mismatch
Risk estimates can differ depending on whether breast density is included and which density category is used. Avoid mixing estimates across versions without documenting the change.
Pedigree under-capture
A sparse family history may underestimate risk, especially when paternal relatives, unaffected relatives, or ages at diagnosis are missing.
Known hereditary syndrome
If a pathogenic variant is known or strongly suspected, use genetics-specific assessment and guideline pathways rather than relying on a screening-risk number alone.
Threshold overconfidence
A lifetime risk near a threshold should be interpreted with sensitivity to input uncertainty, local policy, and patient preferences.
6. Practical Scenarios
Dense breasts plus a second-degree family history
Tyrer-Cuzick can be appropriate because it can incorporate density and family history. Document the density category and relatives entered, then apply the imaging program's MRI threshold rules.
Atypical hyperplasia on biopsy
Both Gail and Tyrer-Cuzick may be clinically useful. Gail may support a 5-year chemoprevention conversation, while Tyrer-Cuzick may better support lifetime-risk screening triage, especially if density and family history are relevant.
Young-onset breast cancer in multiple relatives
Tyrer-Cuzick may flag high lifetime risk, but CanRisk/BOADICEA and formal genetics assessment are usually more appropriate for carrier probability and hereditary syndrome evaluation.
7. Frequently Asked Questions
What risk threshold is considered high risk for MRI?
Many screening recommendations use a lifetime breast cancer risk around 20% to 25% or greater from family-history-based tools as a high-risk MRI threshold. Exact eligibility varies by guideline, country, payer, and local protocol.
Can Tyrer-Cuzick be used for a woman with prior breast cancer?
Use caution. Many breast risk models are designed for estimating future first primary breast cancer risk in unaffected women. Survivorship surveillance and contralateral-risk questions may require different evidence and specialist guidance.
Why did the risk increase after adding breast density?
Dense breast tissue is both a risk factor and a factor that can reduce mammographic sensitivity. Current IBIS implementations that include density may therefore produce higher estimates than calculations that omit density.
Should I use Tyrer-Cuzick or CanRisk for genetic testing eligibility?
If the decision is specifically genetic testing or carrier probability, CanRisk/BOADICEA or a genetics service pathway is often more appropriate. Tyrer-Cuzick may still be used by some clinics for screening-risk documentation.
Use IBIS When Screening Risk Needs More Detail
Pair Tyrer-Cuzick with Gail/BCRAT for chemoprevention context and CanRisk/BOADICEA for genetics-oriented questions.
Open Breast Cancer ToolsReferences
- IBIS Risk Assessment Tool v8.0b. Source
- Risk Evaluator Software. IBIS Breast Cancer Risk Evaluation Tool and density update references. Source
- Warwick J, et al. Mammographic breast density refines Tyrer-Cuzick estimates of breast cancer risk in high-risk women. Breast Cancer Res. 2014;16:451. Source
- National Cancer Institute. Breast Cancer Risk Assessment Tool for Gail/BCRAT comparison. Source
- CanRisk official tool for BOADICEA comparison. Source
- American Cancer Society. Breast cancer screening recommendations for women at high risk. Source
- Distribution of estimated lifetime breast cancer risk among women undergoing screening mammography. Source