Histopathology of subcutaneous tumors formed after the inoculation of LM38 sublines into syngeneic mice. Tumor sections were stained with hematoxylin and eosin (upper panels) or by an immunohistochemistry procedure, for α-smooth muscle actin (α-SMA; middle panels), for pancytokeratins (pan-CK; left and central lower panels) or for cytokeratin 14 (CK14; right lower panel). The LM38-LP cells (left panels) formed differentiated papillary adenocarcinomas made up of cells positive for α-SMA and pan-CK surrounding fibrovascular strands. In contrast, the LM38-HP cells (central panels) formed poorly differentiated adenocarcinomas with no evidence of glandular structures, that were made up of cells mostly negative for both cell lineage markers. The LM38-D2 clone (right panels) grew as an undifferentiated tumor consisting of large cells positive for CK14 and α-SMA. (Original magnification ×400; scale bar, 35 μm.) E, epidermis; F, hair follicle; N, necrosis; S, fibrovascular stroma; T, tumor tissue.