Ma)ignant Basal Cell Tumor in a Iljungarian Hamster

A malignant basal cell tumor was found in the skin of the abdornen of a female Djungarian hamster of unknown age and weighing 40 g. Histologically. the tumor mass was composed ef cells resembling the basal cells of the epiderrnis, and these cells exhibited solid type preliferation. In the tumor tissue and necrotic foci, horn cysts were observed. Irnrnunohistochemically. cytokeratin was present in the tumer cells and horncysts, By electron microscepic examination, the tumor cells had seanty cell organelles and a few desmozomeS. This paper describes a rare malignant ba$al cell tumor in a Djungarian hamster.-KEy woRDs: Djungarian hamster, malignant basal cell tUMOT. J, Vet, Med. Sci. 61(2): l91-193, 1999 Basal cell tumors are common benign tumors in dogs and cats [3, 10], whereas malignant basal cell turnors have infrequently been found in dogs [4]. Spontaneous tumors in hamsters are uncommon, and skin tumors rarely occurred in hamster [9]. According to the classification of basal cell tumors, there is a basosquamous variety sometimes with foci of keratinization [l21, We report here a rare case that was diagnosed as malignant basal cell tumor with basosquarnous varieties as a result of histological, immunohistochemical and clectron microscopic examinations of a mass in the abctominal skin of a Djungarian hamster. In a Djungarian hamster of unknown age and weighing 40 g, a mass of about 4,8 × 3.5 × 1.8 cm was found in the abdominal skin, The hamster died the day after extirpation of the mass. After fixation in 10% buffered formalin, tissue from the mass was ernbedded in paraffin wax, cut into sections, and stained with hematoxylin and eosin(HE), and Masson's trichrome. Other sections were used for immunohistochemical staining, and processed for the streptayidin biotin (SAB-PO) method using a SAB-PO kit (NICHIREI, Tokyo), Primary antibodies used were antihuman keratinlcytokeratin (NICHIREI, Tokyo). For electron microscopy, formalin-fixed tissue pieces were refixed in 1% glutaraldehyde and 4% formalin. and postfixed in 1 % osmium tetroxide O.1 M cacodylic acid buffor fixative solution, The samples were processed routinely and embedded in epoxy resin. Ultrathin sections were cut, stained with uranylacetate and lead citrate, and examined with an electron microscope (JEM 1200 EX). Macroscopically, the mass was about the size of a smali egg, and its surface assumed a color of yel]owish gray. The cut surface was subdivided into lobules by fibrous tissue. Microscopically, the mass was composed of a solid proliferation of cells resembling the basal cells of the * CoRREspoNDENcE To: SATo, T., Department of Veterinary Pathelogy, College of Bioresour¢ e Sciences, Nihon University, 1866 Kameino, Fujisawa, Kanagawa 252-8510, Japan. epidermis. These turnor cells were large, and they had an orbicular or oval hyperchromatic nu leus, The cytoplasm was scant and the rnitoses were numerous (Fig. 1). Masson's trichrome stain, revealed that he connective tissue subdiyided the mass into lobules. At the verge of the lobules, the tumor cells exhibited a fence-like arrangement. Large necrotic foci were present in the central and surrounding areas of these lobules (Fig. 2). Marked neutrophil infiltration and calcification were obseryed in the necrotic foci. Occasionally, spindle ceils with dark nuclei were found at the verge of the necrotic areas, Horn cysts with squamatization existed in these lobules and necrotic foci (Fig. 3), Immunohistochemically, the tumoT cells (Fig. 4) and the horn cysts (Fig. 5) were positiye for cytokeratin. Electron microscopy revealed the large pale nuclei and scanty cell organelle in the turnor cells. The cytoplasm was filled with numerous free ribosomes, A moderate amount of chromatin clurnpings was present in the nucleoplasm. A sma}1 number of desmosomes were detected (Fig. 6). Basal cell tumors arise from cells resembling the basal cells of the epideumis and its appendages [S], Most basal cell tumors can bc subclassified on the basis of their histological ppearance, and they have been subdivided into solid, cystic, ribbon (adenoid), and medusoid types [10], Usually, they are slow growing, noninvasive, often encapsulated, and rarely metastasize, But the solid basal cell tumors are mote aggressive than the other histological types [6, 10], Fukui et at. [41 reported two cases of canine malignant basal cell tumor. One of them occurred in the abdominal skin, showed fast growth, and its histological pattern was the solid and adenoid types. In this case, pulmonary and adrenal metastases were noted. The other tumor originated from the skin of cervical area and showed a keratinizing tendency and severely invaded the surrounding tissues. Since the Ibjungarian hamster examined by us died the day after excision of the mass, the recurTence, metastasis and growth rate of the tumor were unknown. HistologicalIy, however, this tumor showed aggressive solid type proliferation, and horn cysts were present, similar to those malignant basal cell tumors reported by Fukui et at. Japanese Society of Veterinary Science NII-Electronic Library Service apanese oolety f terlnary olenoe 192 K .NAKAO , T, SATO , W . SHIRAI AND K . MATSUO 工工 一leotronlo lbra y Japanese Society of Veterinary Science NII-Electronic Library Service apaneseSociety fVeterinary cience DJUNGARIAN HAMSTER MALIGNANT BASAL CELL TUMOR 193 [4]. In immunohistochemical staining, we used the primary antibodies that react extensively with keratin to deterrnine the distribution f keratin in the present tumor [2, 8], As a result, the tumor cells and horn cysts were positive for cytokeratin. The existence of cytokeratin is・characteristic of basal cell tumor, and cytokeratin seems to exist in different squamous cell nests [8, 1 1], Electron microscopy demonstrated that tumor cells in the present case resembled the basal cells of the epiderrnis, shdwing scanty cell organelles and a large amount of free ribosomes gn the cytoplasm. Chromatin clumps werc distributed in the nucleoplasm, and a small number of desmosomes were observed [1,7]. It thus appeared that electron microscopy confirmed and extended the results obtained by the light rnlcroscoplcexamlnatlons.