This lesion is a disorganized proliferation of suboptimally differentiated glandular epithelium. The latter is characterized cytomorphologically as basaloid (glandular epithelial reserve cells) generally with a small quantity of basophilic-staining, amorphous cytoplasm surrounding an ovoid to laterally flattened nucleus. Marginated chromatin creates an open-faced/vesicular appearance and exposes nucleoli variable, influenced by the density of cellular compaction versus slight dissociation. There is occasional differentiation of these glandular epithelium reserve cells into larger more lightly eosinophilic-staining secretory glandular epithelial cells. Mitoses are present but relatively infrequent, identified in the average incidence of less than one mitotic spindle per standard quantitated microscopic surface area of 10 consecutive 400 x high-power magnification fields. The glandular epithelium exists in multiple forms, including compactly cellular nests and columns. These occasionally differentiate into rudimentary acini and tubules characterized by reasonably good to poor cellular polarity with considerable cellular crowding and piling.
Tubuloglandular basement membrane circumscription is inconsistent and incomplete. Therefore, there is multifocal disorganized infiltration of the intralesional fibrous connective tissue stroma by the neoplastic epithelium. The lesion contains several micro-and micro-cavitary chambers into which there are disorganized papilliferous proliferations of epithelium. The mass enlarges by both expansion and local infiltration, although the majority of the latter occurs within the interior of the mass rather than around its periphery. Nevertheless, there are a few small satellite nests of neoplastic glandular epithelium surrounding the primary tumor nodule.
Foci of liquefactive necrosis are non-inflammatory. The lesion is restricted to the subcutis. It appears to be confined with biopsy margins, although the peripheral border of normal clean connective tissue surrounding this mass is variable from moderately generous to extremely thin. In some instances the neoplastic glandular epithelium and the biopsy margins appear to coincide. However, there is no evidence of either intra- or peri-lesional vascular infiltration.
Mammary adenocarcinoma, papillary/cystic with multifocal necrosis and perilesional satellite neoplastic nodules.
The axillary region is a common site for mammary glandular epithelium in rodents with potential for neoplastic transformation in the axillary, lateral thoracoabdominal, and flank regions as well as the ventral abdomen. The lesion is sub-classified as a moderate grade malignancy on the basis of cellular undifferentiation, disorganization, necrosis, and invasive growth, although the majority of the latter appears to occur with the intra-lesional supporting fibrous trauma rather than the perilesional subcutis. However, there are a few small satellite nodules around the periphery of the main mass (local perilesional metastases). The thickness of the surgical margin is variable from moderate to minimal with neoplastic glandular epithelium focally extending extremely close to and focally reaching the biopsy margins. Clinical behavior is sometimes more aggressive than might be expected based upon microscopic features such as these. Clinical options might include prophylactic deeper excision or at least very close conservative observation of the surgical site. Lesions of this type have a variable potential for metastasis, the likelihood which is unknown.
Photo on left shows preparing to remove mass. The photo on the right shows the extent of the area from which mass was removed.
Photo on left shows mass (confirmed adenocarcinoma). The photo on right shows closed incision site and Petunia being recovered.
Veterinary Surgeon: Kimberly Somjen,DVM
Pathologist: Ken Mero,DVM, PhD
Case history & photos: Branwen Resop
Posted on July 26, 2012, 12:22,
Last updated on January 7, 2013, 16:09