Topographic enhancement mapping of the cancer-associated breast stroma using breast MRI

Abstract

In animal and laboratory models, cancer-associated stroma, or elements of the supporting tissue surrounding a primary tumor, has been shown to be necessary for tumor evolution and progression. However, little is understood or studied regarding the properties of intact stroma in human cancer in vivo. In addition, for breast cancer patients, the optimal volume of local tissue to treat surrounding a primary tumor is not clear. Here, we performed an interdisciplinary study of normal-appearing breast tissue using breast magnetic resonance imaging (MRI), correlative histology and array comparative genomic hybridization to identify a cancer-associated stroma in humans. Using a novel technique for segmenting breast fibroglandular tissue, quantifiable topographic percent enhancement mapping of the stroma surrounding invasive breast cancer was found to be significantly elevated within 2 cm of the tumor edge. This region was also found to harbor increased microvessel density, and genomic changes that were closely associated with host normal breast tissue. These findings indicate that a cancer-associated stroma may be identified and characterized in human breast cancer using non-invasive imaging techniques. Identification of a cancer-associated stroma may be further developed to help guide local therapy to reduce recurrence and morbidity in breast cancer patients.

Fig. 1

Tumor voxels are separated from normal-appearing breast following segmentation of fibroglandular breast tissue. (Left) Mid-sagittal cuts from pre- and post- contrast images are shown from a malignant tumor-bearing breast. (Middle) A fuzzy c-means based algorithm is applied to segment the fibroglandular breast tissue compartment. (Right) Voxels that represent malignant tumor are further segmented from normal-appearing fibroglandular breast tissue by percent enhancement threshold of >70%.

Fig. 2

A 3-dimensional topographic map was created based on the proximity of each normal breast tissue voxel from its nearest neighboring tumor voxel. (A) Tumor voxels, identified by PE > 70%, are shown in red, while normal breast tissue voxels, identified by PE < 70%, are shown in green. Numbers written in each green box in the schema show the distance in millimetres of the green voxel to its closest red voxel. (B) Mean percent enhancement was significantly higher at the tumor edge, and decreased with distance through the fibroglandular breast tissue. Pairwise comparisons with Tukey’s adjusted p-values indicated that the mean enhancement at 0–1 cm (p = <0.0001) and at 1–2 cm (p = 0.006) from the edge of the MBL was significantly higher than farther distance intervals.

Fig. 3

Microvessel density quantified by CD31 immunohistochemistry was compared between tissue sections close (within 2 cm) and far (>2 cm) of the tumor edge. Micrograph showing CD 31 immunohistochemistry in (a) near and (b) far tissue sections. (c) The mean MVD for breast tissue <2 cm from the IBC (80 vessels mm⁻², 95% CI : 61–98) was found to be significantly higher than the mean MVD in breast tissue >2 cm from the IBC (54 vessels mm⁻², 95% CI : 36–72, p = 0.04 for two-sided t-test).

Fig. 4

Thin sections from near and far tissue blocks were microdissected for genomic array analysis. (A) A hematoxylin and eosin stained section shows tumor (black outline) and surrounding stroma. (B) Cresyl green stain showing stromal elements. (C) Non-epithelial normal tissue was microdissected. (D) Normal epithelium was isolated from all other stromal elements.

Fig. 5

Array comparative genomic hybridization was performed on tumor, adjacent stroma and stroma far from the tumor in 3 cases. Representative genome wide changes are depicted with mean values in yellow, gains in blue and losses in red. Compared to tumor, stroma adjacent to and far from the tumor harbored significantly less chromosomal changes than that in the tumor.