An incisional biopsy is performed and microscopic examination reveals a partially encapsulated proliferation of epithelial cells arranged in trabeculae, cords, and nests. In many areas there is formation of tubular or ductal structures lined by cuboidal epithelial cells (Figure 2).

Figure 2.  A low-power photomicrograph depicts a proliferation of epithelial cells forming trabeculae, cords, and nests with focal formation of ductal or tubular structures. (Hematoxylin and eosin stain, original magnification 100x)

Other areas are comprised of collections of ovoid cells with rounded, eccentric nuclei and eosinophilic cytoplasm.  There is a variable stromal background ranging from densely hyalinized areas to lightly staining, myxochondroid areas (Figure 3).  No obvious cellular pleomorphism, mitotic activity, or necrosis is identified.

Figure 3.  The tumor exhibits variation in stromal background and cellularity.  A lightly staining, myxochondroid area with low cellularity is seen in the lower portion of the field, and an eosinophilic, hyalinized area with greater cellularity is seen in the upper portion of the field. (Hematoxylin and eosin stain, original magnification 200x)