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6th International Workshop on Breast Densitometry and Breast ...

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6 th <str<strong>on</strong>g>Internati<strong>on</strong>al</str<strong>on</strong>g> <str<strong>on</strong>g>Workshop</str<strong>on</strong>g> <strong>on</strong> <strong>Breast</strong> <strong>Densitometry</strong><br />

<strong>and</strong> <strong>Breast</strong> Cancer Risk Assessment<br />

CIRRUS: A FULLY-AUTOMATED SOFTWARE PLATFORM FOR BREAST CANCER RISK<br />

PREDICTION FROM MAMMOGRAMS<br />

Daniel F. Schmidt, Enes Makalic, Tu<strong>on</strong>g L. Nguyen, Laura Baglietto, Kavitha Krishnan, Jennifer St<strong>on</strong>e,<br />

Carmel Apicella, Melissa C. Southey, Dallas R. English, Graham G. Giles, John L. Hopper<br />

Centre for Molecular, Envir<strong>on</strong>mental, Genetic <strong>and</strong> Analytic Epidemiology, The University of Melbourne,<br />

Carlt<strong>on</strong> VIC 3053, Australia<br />

Background: There is informati<strong>on</strong> in mammograms, apart from the detecti<strong>on</strong> <strong>and</strong> masking of existing<br />

lesi<strong>on</strong>s, that predicts breast cancer risk. This c<strong>on</strong>cept is currently referred to as ‘mammographic density’,<br />

operati<strong>on</strong>ally defined by the total area of the mammographic image that appears light or white. The most<br />

comm<strong>on</strong>ly used software tool for measuring mammographic density is CUMULUS, a computer-assisted<br />

technique that derives the pixels in a digitised mammogram which corresp<strong>on</strong>d to user-determined<br />

‘mammographically dense regi<strong>on</strong>s’. CUMULUS measures of mammographic density, adjusted for age<br />

<strong>and</strong> body mass index, have been shown to predict breast cancer risk even after adjusting for other<br />

measured breast cancer risk factors.<br />

We have developed a fully-automated predictor of breast cancer risk from digitised mammographic<br />

images, which we call CIRRUS, that does not try to measure ‘mammographic density’ per se, but instead<br />

tries to identify agnostically the features in a mammographic image that best predict breast cancer risk.<br />

Methods: CIRRUS is based <strong>on</strong> image processing <strong>and</strong> machine learning techniques. It includes fully<br />

automated image cropping procedures which remove irrelevant features (e.g. pectoral muscle). In additi<strong>on</strong><br />

to the brightness of the pixels, CIRRUS uses informati<strong>on</strong> from other features in the mammogram, such as<br />

patterns <strong>and</strong> texture.<br />

CIRRUS was trained using 2,597 mammograms (608 cases <strong>and</strong> 1,989 c<strong>on</strong>trols) collected by the<br />

Melbourne Collaborative Cohort Study. Bayesian logistic regressi<strong>on</strong> with the ridge penalty was used to<br />

combine all the extracted image features into the final CIRRUS measure, which was compared with dense<br />

area <strong>and</strong> percent dense area measurements obtained using CUMULUS. The bootstrap technique was used<br />

to estimate the c<strong>on</strong>fidence intervals for the area under the receiver operator curve (AUC). We also<br />

measured CIRRUS for 544 m<strong>on</strong>ozygotic twin pairs (MZ), 339 dizygotic twin pairs (DZ) <strong>and</strong> 1,556 of<br />

their sisters from the Australian Mammographic Density Twins <strong>and</strong> Sisters Study, <strong>and</strong> analysed familial<br />

aspects under a multivariate normal model.<br />

Results: In terms of breast cancer risk predicti<strong>on</strong>, for both dense area <strong>and</strong> percent dense area measured by<br />

CUMULUS the mean AUC was 0.58 (CI 95%: 0.57 – 0.61). For the CIRRUS measure the AUC was 0.62<br />

(CI 95%: 0.58 - 0.64). CIRRUS measures were not markedly associated with age or any other measured<br />

breast cancer risk factor, which explained

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