HCMV in situ hybridization in infiltrating ductal carcinoma. Two examples of HCMV ISH staining from two different patients with infiltrating ductal carcinoma are displayed. Low and high power images of the first patient (a, 40×; b, 100×) demonstrate heterogeneous pattern of detection of HCMV nucleic acids in the nuclei (dark blue) and cytoplasm (light blue) in infiltrating tumor cells but no significant nucleic acid detection in the intervening stroma. Two images from another example of infiltrating ductal carcinoma (c, d; 100×) also reveal areas of HCMV nucleic acid detection in nuclear (dark purple) and cytoplasmic (light purple) areas, without any significant nucleic acid detection in the intervening stroma. Positive control probe specific for DNA Alu repeats from the same case reveals intense (dark purple) nuclear probe hybridization with nucleic acids in infiltrating tumor nuclei and intervening stromal cells, without evidence of cytoplasmic staining (e, 100×). Hybridization signal of a negative control probe specific to insect nucleic acids is completely absent in tumor tissues (f, 100×). Positive control (HCMV infected lung) is positive for HCMV nucleic acid hybridization in scattered pneumocytes (blue cells in g, 100×), while negative control probe is not detected in the same specimens (h, 100×; light hematoxylin counterstain was used in g and h). Low power image (i, 40×) of normal breast epithelium (from reduction mammoplasty) that was negative for HCMV nucleic acid hybridization reveals no hybridization signal. High power (j, 100×) image of normal breast epithelium from reduction mammoplasty reveals faint purple hybridization signal in scattered normal ductal epithelial cells.