Figure 5.b Histologic features of breast cancer biopsies can be recognized and parsed based on gene expression patterns. Enlargements of the regions of the cluster diagram in Figure 4 showing gene clusters enriched for genes expressed in different cell types in the breast cancer specimens, as distinguished by clustering with the cultured cell lines. (A). A cluster including many genes characteristic of epithelial cells, expressed in estrogen-receptor-positive breast cancer derived cell lines (T47D and MCF7) and tumors. (B). Genes expressed in breast cancer derived cell lines with stromal cell characteristics (Hs578T and BT549) and tumor specimens. Expression of these genes in the tumor samples may represent the presence of myofibroblasts in the cancer specimen stroma. (C). Genes expressed in leukocyte-derived cell lines, showing common leukocyte, and separate "myeloid" and "B-cell" gene clusters. (D). Genes that were relatively highly expressed in all cell lines compared to the tumor specimens and normal breast. The higher expression of this set of genes involved in cell cycle transit in the cell lines is likely to reflect the higher proliferative rate of cells cultured in the presence of serum as compared with the average proliferation rate of cells in the biopsied tissue.