Cutaneous mast cell tumours in a lion (Panthera leo): a light and transmission electron microscopical study

Cutaneous mast cell tumours in a lion (Panthera leo): a light and transmission electron microscopical study

J. Comp. Path. 1995 Vol. 113, 291-294 SHORT PAPER C u t a n e o u s M a s t Cell T u m o u r s in a Lion (Panthera leo): a Light a n d T r a n s m i...

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J. Comp. Path. 1995 Vol. 113, 291-294

SHORT PAPER

C u t a n e o u s M a s t Cell T u m o u r s in a Lion (Panthera leo): a Light a n d T r a n s m i s s i o n Electron M i c r o s c o p i c a l Study M. Stolte and M. Welle*

Institute for Zoo Biology and Wildlife Research, PF 1103, 10252 Berlin and *Institute for Veterinary Pathology, Strafle 518 Nr. 15, 14163 Berlin, Germany Summary

Cutaneous mast cell tumours of a 16-year-old female Indian lion (Panthera leo) were studied histologically and ultrastructuraUy. The proliferation index detected with an antibody against the nuclear antigen Ki-67 was 16"5%. A cytochemical test for chymase activity was negative, Mast cell tumours are well known in domestic animals and in cats are of two distinct histological types. The present paper is the first report of poorly differentiated cutaneous mast cell tumours in a lion. In their histological and ultrastructural appearance, and in their lack of chymase activity, the neoplastic mast cells resembled tumour mast cells in cats. 9 1995AcademicPressLimited

In a survey of necropsy reports, Ippen (1987) observed that only 50 of 636 (7"9%) non-domesticated Felidae exhibited tumorous lesions; no data on the incidence of skin tumours were available. Cutaneous mast cell tumours account for 2 - 1 5 % of all skin tumours in domesticated cats. T h e y are found as solitary, multiple or diffuse lesions of the skin (Brown and Chalmers, 1990) and are of two distinct histological types. O n e type occurs primarily in young Siamese cats as subcutaneous nodules o f histiocyte-like cells, with faint cytoplasmic granularity revealed by staining with toluidine blue; tumours of this type appear benign and may regress spontaneously (Wilcock et al., 1986). The second histological type, termed mast cell mastocytoma, is characterized by discrete dermal masses composed of slightly atypical mast cells. Cytoplasmic metachromatic granules are usually observed with toluidine blue staining, but in poorly differentiated tumours such granules may be difficult or impossible to demonstrate. There is also considerable variation in cell and nuclear size. T u m o u r s of the second type occur in older cats and have a low potential for recurrence and metastasis after complete surgical removal. However, anaplastic variants may recur or spread (Moulton, 1990). The present report concerns a 16-year-old female Indian lion (Panthera leo), with more than 20 skin tumours, which was humanely destroyed. The lesions appeared as hairless, occasionally ulcerating, nodules, 1 to 5 cm in diameter. At necropsy no other pathological findings were observed. Samples of the skin 0021-9975/95/070291 +04 $12.00/0

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tumours and internal organs were fixed in formalin and embedded in paraffin wax for histopathological examination. Sections (5 ~tm) of skin tumours were stained with haematoxylin and eosin (HE) and with methylene blue to demonstrate the metachromatic reaction of mast cell granules. The presence of chymase, a mast-cell-specific protease, was tested with naphthol-AS-Dchloroacetate as substrate. Proliferative activity of the tumour cells was estimated with monoclonal antibody MIB 1 (against the Ki-67 antigen) and "visualized" by the alkaline phosphatase-antialkaline phosphatase complex (APAAP) method. In addition, samples of the tumours were fixed in 3% glutaraldehyde for transmission electron microscopy (TEM). Semi-thin sections were stained with toluidine blue and ultra-thin sections with lead citrate and uranyl acetate. On the basis of previous findings in domestic cats, the skin lesions of the lion were classified as poorly differentiated mast cell tumours. The tumours were covered by intact or ulcerated epidermis, with neoplastic cells extending in dense sheets from the stratum papillare deep into the corium, thus forming epidermal nodules. Only a few, atrophic hair shafts remained. The tumours were composed of uniform round to polygonal cells in a fibrovascular stroma. Sparse eosinophils and lymphoid aggregates were present between the tumour cells. The nuclei were large and pleomorphic with one to several nucleoli. Normal mitotic figures were found but were not numerous. Some multinucleated cells were observed. Granulation of the cytoplasm was clearly seen in semi-thin sections (Fig. 1). In these tumours only a few groups of mast cells showed a distinct metachromatic reaction with toluidine blue staining. The test for chymase activity in the tumour mast cells of the lion gave a negative result. This accorded with findings in cats (M. Welle, unpublished) and in cattle (Proske and Welle, 1993), species that, unlike man, dogs and rodents (Caughey et al., 1988), show no chymase activity in skin mast cells. The proliferation index, detected with an antibody directed against the nuclear antigen Ki-67, which is expressed in all active stages of the cell cycle, was 16"5 %. This value was comparable with that of solitary mast cell tumours of dogs (Norma Leschber, personal communication). The ultrastructural features resembled those previously reported in neoplastic mast cells from cats. Most of the tumour cells possessed characteristic granules (Fig. 2) which were enclosed by a membrane and frequently contained finely to coarsely granular contents. Some had cord-like structures. Occasional granules had homogeneous or concentrically arranged contents. The mitochondria contained cristae and occasional vesicular structures. The nuclei varied in size and shape and frequently showed invaginations. Perinuclear areas of fibrils occurred (Fig. 3). The cytoplasm contained numerous small vesicles originating from the well-developed Golgi apparatus, granular endoplasmic reticulum and free ribosomes. Small vesicles containing an electrondense body (Fig. 4) were thought to represent preliminary stages in the formation of mast cell granules. As in cats, it has been reported that mature mast cell granules are homogeneous, electron dense and finely granular (Ward and Hurwitz, 1972), the ultrastructural findings supported the histological observation of poorly differentiated mast cells.

C u t a n e o u s Mast Cell T u m o u r s in a Lion

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@ Fig. 1. Cutaneous mast cell tumour in a lion. Round to polygonal mast cells with characteristic granules (arrow). Semithin section, toluidine blue. Bar = 60 gm. Fig. 2. Typical granules of the neoplastic mast cells. Ultrathin section, TEM. Bar= 0"4 gm. Fig. 3. Area of intracytoplasmic fibrils (arrow) and mitochondrium (M) of a neoplastic mast cell. Ultrathin section, TEM. Bar=0"4 gin. Fig. 4. Cytoplasm of a neoplastic mast cell with Golgi apparatus (G) and vesicles, one with electrondense contents (arrow). Ultrathin section, TEM. Bar = 0'4 gm.

I n c o n c l u s i o n , t h e c u t a n e o u s m a s t cell t u m o u r s o f t h e l i o n r e s e m b l e d , histologically, ultrastructurally and in their lack of chymase activity, mast cellt y p e m a s t o c y t o m a s o f d o m e s t i c cats. N o m e t a s t a s i s i n t o l y m p h n o d e s o r internal organs was observed. However, because of the large number of the c u t a n e o u s t u m o u r s a n d t h e p o o r l y d i f f e r e n t i a t e d m a s t cells, m a l i g n a n c y w i t h widespread metastasis within the skin could not be ruled out. Acknowledgments

W e t h a n k D. Viertel, M. Biering a n d D. R e h a h n for their technical support. References

Brown, C. A. a n d C h a l m e r s , S. A. (1990). Diffuse cutaneous mastocytosis in a cat. Veterinary Pathology, 27, 366-369.

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Caughey, G. H., Viro, N. F., Lazarus, S. C. and Nadel, J. A. (1988). Purification and characterization of dog mastocytoma chymase: identification of an octapeptide conserved in chymotryptic leucocyte proteinases. Biochimica et Biophysica Acta, 952, 142-149. Ippen, R. (1987). Ein Beitrag zu den Tumeron der nicht-domestizierten Landraubtiere (Fissipedia). Deutsche 7~eri~rztliche Wochenschrifi, 94, 61-63. Moulton, J. E. (1990). Tumours in Domestic Animals, 3rd Edit., J. E. Mouhon, Ed., University of California Press, California, p. 43. Proske, S. and Welle, M. (1993). Nachweis yon Tryptase in bovinen Mastzellen. Berliner und Miinchener 7~eriirztliche Wochenschrifi, 106, 390. Ward, J. M. and Hurwitz, A. I. (1972). Ultrastructure of normal and neoplastic mast cells of the cat. VeterinaryPathology, 9, 202-211. Wilcock, B. P., Yager, J. A. and Zink, M. C. (1986). The morphology and behaviour of feline cutaneous mastocytomas. VeterinaryPathology, 23, 320-324.

I Received, Februa(y 8th, 1995] Accepted, May 15th, 1995 ]