Optical breast cancer margin assessment: an observational study of the effects of tissue heterogeneity on optical contrast

INTRODUCTION: Residual cancer following breast conserving surgery increases the risk of local recurrence and mortality. Margin assessment presents an unmet clinical need. Breast tissue is markedly heterogeneous, which makes distinguishing small foci of cancer within the spectrum of normal tissue potentially challenging. This is further complicated by the heterogeneity as a function of menopausal status. Optical spectroscopy can provide surgeons with intra-operative diagnostic tools. Here, we evaluate ex-vivo breast tissue and determine which sources of optical contrast have the potential to detect malignancy at the margins in women of differing breast composition. METHODS: Diffuse reflectance spectra were measured from 595 normal and 38 malignant sites from the margins of 104 partial mastectomy patients. All statistical tests were performed using Wilcoxon Rank-Sum tests. Normal and malignant sites were compared before stratifying the data by tissue type and depth and computing statistical differences. The frequencies of the normal tissue types were separated by menopausal status and compared to the corresponding optical properties. RESULTS: The mean reduced scattering coefficient, < μ(s)' >, and concentration of total hemoglobin, [THb]), showed statistical differences between malignant (< μ(s)' > : 8.96 cm(-1 )± 2.24(MAD), [THb]: 42.70 μM ± 29.31(MAD)) compared to normal sites (< μ(s)' > : 7.29 cm(-1 )± 2.15(MAD), [THb]: 32.09 μM ± 16.73(MAD)) (P < 0.05). The sites stratified according to normal tissue type (fibro-glandular (FG), fibro-adipose (FA), and adipose (A)) or disease type (invasive ductal carcinoma (IDC) and ductal carcinoma in situ (DCIS)) showed that FG exhibited increased < μ(s)' > and A showed increased [β-carotene] within normal tissues. Scattering differentiated between most malignant sites, DCIS (9.46 cm(-1 )± 1.06(MAD)) and IDC (8.00 cm(-1 )± 1.81(MAD)), versus A (6.50 cm(-1 )± 1.95(MAD)). [β-carotene] showed marginal differences between DCIS (19.00 μM ± 6.93(MAD), and FG (15.30 μM ± 5.64(MAD)). [THb] exhibited statistical differences between positive sites (92.57 μM ± 18.46(MAD)) and FG (34.12 μM ± 22.77(MAD)), FA (28.63 μM ± 14.19(MAD)), and A (30.36 μM ± 14.86(MAD)). The diagnostic ability of the optical parameters was affected by distance of tumor from the margin as well as menopausal status. Due to decreased fibrous content and increased adipose content, normal sites in post-menopausal patients exhibited lower < μ(s)' >, but higher [β-carotene] than pre-menopausal patients. CONCLUSIONS: The data indicate that the ability of an optical parameter to differentiate benign from malignant breast tissues may be dictated by patient demographics. Scattering differentiated between malignant and adipose sites and would be most effective in post-menopausal women. [β-carotene] or [THb] may be more applicable in pre-menopausal women to differentiate malignant from fibrous sites. Patient demographics are therefore an important component to incorporate into optical characterization of breast specimens.