# Tumour size on a breast report, and why it differs from the scan

Source: https://onco.cc/terms/breast-tumour-size-on-the-report/  
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## TL;DR

The size on the pathology report is the largest continuous lump of invasive cancer measured under the microscope, which is not the same as the size on the mammogram or the MRI. Separate deposits five millimetres or more apart are not added together, and the in-situ disease around the tumour is measured separately.

## Summary

Size matters because it is a prognostic factor in its own right, a component of the Nottingham Prognostic Index and of PREDICT, and the T of the TNM category. The dataset asks for the maximum dimension of the invasive tumour in millimetres, measured macroscopically in the fresh or fixed specimen and microscopically where the borders are diffuse, with the microscopic measurement treated as the gold standard. The report gives the invasive size and, separately, the whole tumour size including any in-situ disease extending beyond it, because those two numbers answer different questions: the first feeds the stage and the prognosis, the second tells the surgeon how much has to come out.

Three rules explain most discrepancies a patient notices. Satellite deposits are not included in the maximum invasive dimension, and neither are foci of lymphovascular invasion or cells displaced along a needle track; the dataset says no distance can be defined that settles whether two nearby foci are one tumour cut in two planes or two tumours, but that if they are 5 mm or more apart they are unlikely to be one. Where the cancer was removed entirely by the needle or vacuum biopsy, the pathologist goes back to that specimen and estimates, and says that the estimate is likely to be inaccurate although the cancer was certainly small. And where size cannot be measured at all, the fallback order is the imaging size, MRI first, then ultrasound, then mammography, and last and least accurate the clinical size.

It is worth knowing how imprecise this number is. The dataset reports that the national breast screening programme's external quality assurance scheme finds poor concordance between pathologists on tumour size even on ready-prepared slides, which cannot be explained by slide-to-slide variation, and observes that the scope for error must be greater still once the difficulty of dissecting the specimen is added. A tumour reported as 21 mm rather than 19 mm crosses the boundary from T1 to T2, and the measurement is not precise to 2 mm. This is one reason the index and the tools that use size band it rather than treating it as exact.

## Fields

- Kind: Term
- Last checked: 2026-09-25
- Also known as: tumour size breast; invasive tumour size; whole tumour size; maximum dimension; size on the report; satellite focus; multifocal breast cancer; multicentric breast cancer; size discrepancy

## Sources

- Royal College of Pathologists G148: dataset for histopathological reporting of breast disease in surgical excision specimens of breast cancer, version 3, November 2024 (full review due November 2026): https://www.rcpath.org/resourceLibrary/g148-dataset-for-histopathological-reporting-of-breast-disease-in-surgical-excision-specimens-of-breast-cancer.html
- Brierley et al., International Journal of Cancer 2026: the 9th edition of the UICC TNM classification of malignant tumours, updates and rationale for change (breast: the classification remains unchanged, the yp classification is clarified): https://doi.org/10.1002/ijc.70561

## Connected records

- terms: [Grade, stage and receptor status: three different things on one breast report](https://onco.cc/terms/grade-stage-receptor-breast/), [Lymphovascular invasion (LVI)](https://onco.cc/terms/lymphovascular-invasion/), [Nottingham grade (breast cancer grade 1, 2 and 3)](https://onco.cc/terms/nottingham-grade/), [Nottingham Prognostic Index (NPI), and PREDICT](https://onco.cc/terms/nottingham-prognostic-index/), [Resection margins (R0 / R1 / R2)](https://onco.cc/terms/resection-margins/), [Stage](https://onco.cc/terms/cancer-stage/), [Which staging edition a breast report uses: UICC TNM 8, TNM 9 and the AJCC prognostic stage](https://onco.cc/terms/tnm-breast-cancer-editions/)
- technologies: [Mammography & tomosynthesis](https://onco.cc/technologies/mammography/)
- cancers: [Breast cancer (all types)](https://onco.cc/cancers/breast-cancer/), [Ductal carcinoma in situ (DCIS)](https://onco.cc/cancers/ductal-carcinoma-in-situ/), [Invasive breast carcinoma of no special type (invasive ductal carcinoma)](https://onco.cc/cancers/invasive-breast-carcinoma-no-special-type/), [Invasive lobular carcinoma of the breast](https://onco.cc/cancers/invasive-lobular-carcinoma/)
- fronts: [Diagnostics & Biomarkers](https://onco.cc/fronts/diagnostics/)

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