Classification of breast tissue density by optical transillumination spectroscopy: optical and physiological effects governing predictive value.

Preventive oncology is in need of a risk assessment technique that can identify individuals at high risk for breast cancer and has the ability to monitor the efficacy of a risk reducing intervention. Optical transillumination spectroscopy (OTS) gives information about breast tissue composition and tissue density. OTS is noninvasive and in contrast to mammography, uses nonionizing radiation. It is safe and can be used frequently on younger women, potentially permitting early risk detection and thus increasing the time available for risk reduction interventions to assert their influence. Before OTS can be used as a risk assessment and/or monitoring technique, its predictive ability needs to be demonstrated and maximized through the construction of various mathematical models relating OTS and breast tissue density, and hence, risk. To establish a correlation between OTS and mammographic density principal components analysis (PCA), using risk classification, is calculated. The PCA scores are presented in three-dimensional cluster plots and a plane of differentiation that separates the high and low tissue densities is used to calculate the predictive value. Stratification of PCA for measurement position on the breast in cranial-caudal projection is introduced. Analysis of PCA scores as a function of the volunteer's age and body mass index (BMI) is examined. A small but significant correlation between the component scores and age or BMI is noted but the correlation is dependent on the tissue density category examined. Correction of the component scores for age and BMI is not recommended, since a priori knowledge of a woman's breast tissue density is required. Stratification for the center and distal measurement positions provide a predictive value for OTS above 96%.