Malignant Gastrointestinal Stromal Tumor Showing Remarkable Whorl Formations.

Common thinking has been that gastrointestinal stromal tumors (GISTs) do not show distinct smooth muscle or neural differentiation. In many recent studies associated with molecular biology, the cellular origin of GISTs has been regarded as the interstitial cells of Cajal (ICC). In addition, GISTs are thought to occur by gain-of-function mutations of the c-kit gene that are expressed in the ICC.[1] In cellular arrangements of spindle cell-type GISTs, many kinds of patterns have been described. We encountered a GIST showing remarkable whorl formations in the tumor and report herein the interesting ultrastructural features of these tumor cells.

REPORT OF A CASE

A 67-year-old woman noticed an edema of both legs, and the next day an abdominal distension was found by her general practitioner. Three days later, she was admitted to the hospital for a more detailed examination. A duodenal tumor was detected in her abdominal cavity, and on computed tomography, a metastatic liver tumor was also found. Surgical resection to the duodenal tumor was performed.

METHODS

Surgical slides were stained with hematoxylin-eosin. Immunohistochemical studies were performed on paraffin sections by the avidin-biotin-peroxidase complex technique. The antibodies included vimentin (1:50, Dako Corporation A/S, Glostrup, Denmark), S100 protein (1:400, Dako), [Alpha]-smooth muscle actin ([Alpha]-SMA, 1:50; Dako), CD34 (prediluted, Nichirei, Tokyo, Japan), neuron-specific enolase (NSE, 1:100; Dako), CD117 (anti-human c-Kit) (1:50, Dako), and epithelial membrane antigen (EMA, 1:100; Dako). Ultrastructural examination of the tumor cell was also performed with materials obtained from tissue fixed in formalin.

RESULTS

Gross Findings

The encapsulated tumor was 21 x 20 x 12 cm, originated from the transverse portion of the duodenum, was located in the propria muscularis of the wall, and showed extramural proliferation. An uneven, solid dark brown and tan tumor was seen at the cut surface. Massive central necrosis was revealed in the tumor.

Histologic Findings

Remarkable whorl formations were revealed in all areas of the tumor (Figure 1, A), and irregular fascicular patterns were also occasionally seen. The tumor was mainly composed of spindle-shaped cells with faintly eosinophilic cytoplasm and cigar-shaped nuclei. Cellular pleomorphism was sometimes pronounced. Cellularity was high, and mitotic counts were 4 to 5 per 10 high-power fields. Psammoma bodies or skeinoid fibers were not present.

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Immunohistochemistry

Most tumor cells were positive for vimentin and CD117 (Figure 1, B) and weakly positive for CD34. In addition, NSE was positive in a few cells. In contrast, S100 protein, or-SMA, and EMA were all negative.

Ultrastructural Findings

The tumor cells had slender cytoplasmic processes, and the processes formed many interdigitations and desmosome-like structures between tumor cells forming whorled patterns (Figure 2, A and B). These structures were scant in the area showing a fascicular pattern. In the cytoplasm of the tumor cell, abundant free ribosomes were recognized, but Well-developed rough endoplasmic reticula were few (Figure 2, B). Smooth vesicles were found in the cytoplasm, and intermediate filaments were frequently seen in most tumor cells. Basement membranes were inconspicuous. Furthermore, organellas such as focal bundles of actin filaments or small granular vesicles and dense core granules were not found. Many fibrous long-spacing (FLS) collagen fibrils, with a periodicity of approximately 140 to 150 nm, were also recognized between tumor cells (Figure 3, A and B).

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COMMENT

Histopathologically, the tumor in the present case started from the muscular layer and had a proliferation of spindle-shaped cells with remarkable whorl formations. Therefore, we needed to distinguish among myogenic tumors, neurogenic tumors, GISTs, and other mesenchymal tumors derived from gastrointestinal tracts. Immunoreaction for vimentin and CD34 was positive, but both [Alpha]-SMA and S100, as markers of smooth muscle cell and Schwann cell differentiation, were negative. Besides, the tumor cells showed mostly positive reactions in CD117; the c-kit proto-oncogene protein, which includes a tyrosine kinase component, is expressed in and is a useful marker of GISTs.[2,3] According to these findings, we diagnosed the tumor in this case as a GIST not showing obvious smooth muscle or neural differentiation.

In GISTs, many kinds of arrangements in cell clusters other than whorls, such as solid sheets, fascicular, storiform, palisading, herring bone, or organoid, are reported.[2,4] However, case reports of GISTs describing remarkable whorl formations throughout the whole area of the tumor, as in our case, are extremely rare. There is a case report of a gastrointestinal autonomic nerve tumor (GANT), a subpopulation of GISTs, showing organoid or whorls patterns in most areas of the tumor.[5] In this report, there was diffuse immunoreactivity for vimentin and focal reactivity for NSE, findings that resembled our case and also suggested the neural differentiation of the tumor in our case. However, ultrastructurally, the dense core granules or skeinoid fibers recognized in the GANT case were not present in our case. Commonly, GANTs not only form whorl patterns but also diffuse sheet, palisading, fascicular, or storiform patterns. For this reason, it is difficult to conclude that the tumor that shows the whorl patterns of our case has a neural differentiation. Furthermore, many nonepithelial tumors, other than meningioma, that have meningothelial-like whorls associated with spindle-shaped cell proliferation, such as malignant peripheral nerve sheath tumor (MPNST), perineurioma, liposarcoma, and dendritic reticulum cell sarcoma, have been reported. In these tumors, MPNST may occur in the gastrointestinal tract. In MPNST, tumor cells are able to form variable arrangements, such as whorl, curlicue, or nuclear palisading formations, and are, therefore, difficult to distinguish from GISTs. However, immunoreaction for S100 protein is present in 30% to 67% of MPNSTs but generally negative in GISTs,[2,6] as in our case. Whorl patterns are also found in liposarcomas or meningioma, but these tumors derived from the gastrointestinal tract are extremely rare. Perineurioma is generally found in subcutaneous sites and only infrequently affects deep soft tissues of the extremities or trunk. However, our case did not show any immunoreaction for EMA, a diagnostic marker of perineuroma. Regarding the relation between differentiation and whorl patterns, Fanburg-Smith and Miettinen[7] suggested, in a report based on a histopathologic and immunohistochemicat study of 17 cases of liposarcomas with meningothelial-like whorls, that meningothelial whorls might represent an early sign of dedifferentiation of liposarcoma. This report is suggestive of our thinking on the differentiation or pathogenesis of the tumor in our case.

With ultrastructural observations of the intestinal muscle coat of mouse and bat, Yamamoto[8] summarized the character of the ICC as being (1) slender cytoplasmic processes, (2) ample free ribosomes, (3) numerous pinocytotic vesicles, and (4) a basement membrane that incompletely or completely covered them. These findings, other than numerous pinocytotic vesicles, closely resembled those of our case, and so it could be suggested that our case's tumor cells originated from ICC. In the areas with whorl formations of our case, ultrastructurally many more interdigitations and desmosome-like structures were recognized compared with a fascicular pattern. Therefore, these structures might be associated with whorl formations, and according to the degree or quantity of these structures, whorl patterns might be formed. Otherwise, other biological mechanisms, for example, malignant transformations or dedifferentiation, also might be associated with whorl formation. Tumor cells that form the whorl patterns in our case have fine organellas common with those of other tumors. In meningiomas that show whorl patterns, particularly transitional meningioma, interdigitations and/or desmosome-like structures are markedly seen. Conventional MPNSTs, which have the possibility of forming whorl patterns, contain branched cytoplasmic processes covered by basal lamina. In perineurinoma, many organellas resembling our case are found, such as long cytoplasmic processes or discontinuous basement membrane. However, the tumor cells of GISTs in the present case had a scarcity of well-developed rough endoplasmic reticula compared with abundant free ribosomes in the cytoplasm of the tumor cell. It is said that immature or undifferentiated tumor cells have a poor complement of rough endoplasmic reticula.[9] Accordingly, it is reasonable to regard the tumor cells of GISTs as cells having the possibility to differentiate to other organs or tumors in the future.

Another noticeable ultrastructural feature of our case is that a lot of FLS collagen fibrils between tumor cells were recognized in most areas. Such typical FLS collagen fibrils, which occur as long fibrils, showed a periodicity of 140 to 160 nm. Such FLS collagen fibrils have been found in a variety of normal or morbid tissue. The FLS fibrils appear in relation to many tumors, such as schwannoma, astrocytoma, lymphoma, basal cell carcinoma, and melanoma.[9] Hence, the features of FLSs cannot be specific to GISTs but could be of interest if we consider the causality of FLS collagen fibrils and GISTs or the possibility of GISTs producing such collagen. These mechanisms may be revealed with the future accumulation of GIST cases.

In conclusion, our case expands the current range of histologic presentations of GISTs. Additional ultrastructural information helps to understand GISTs, tumors with a confusing history and abundant data, supporting the idea of multiple directions of differentiation. There are benefits in the ultrastructural study of whorls and FLS collagen and the possible commonalties with other tumors, features that contribute to the difficulties in histologic identification.

We thank Dr Yoshihumi Maeda, Division of Surgery, Senbon Hospital, Osaka, Japan, for his kind support.

References

[1.] Hirota S, Isozaki K, Moriyama Y. Gain-of-function mutation of c-kit in human gastrointestinal stromal tumors. Science. 1998;279:577-580.

[2.] Miettinen M, Sarlomo-Rikala M, Lasota J. Gastrointestinal stromal tumours: recent advances in understanding of their biology. Hum Pathol. 1999;30:1213-1220.

[3.] Kindblom LG, Remotti HE, Aldenborg F. Gastrointestinal pacemaker cell tumor (GIPACT): gastrointestinal stromal tumors show phenotypic characteristics of the intestinal cells of Cajal. Am J Pathol. 1998;152:1259-1269.

[4.] Lewin KJ, Appelman HD. Tumors of the Esophagus and Stomach. Washington, DC: Armed Forces Institute of Pathology; 1996. Atlas of Tumor Pathology; 3rd series, fascicle 18.

[5.] Ishimbaldi G, Santagelo M, Cenacchi G, et al. Gastrointestinal autonomic nerve tumor (plexosarcoma): report of a case with fine needle aspiration biopsy and histologic, immunocytochemical and ultrastructural study. Acta Cytol. 1998; 42:1189-1194.

[6.] Scheithauer BW, Woodruff JM, Erlandson RA. Tumors of the Peripheral Nervous System. Washington, DC: Armed Forces Institute of Pathology; 1999. Atlas of Tumor Pathology; 3rd series, fascicle 24.

[7.] Fanburg-Smith JC, Miettinen M. Liposarcoma with meningothelial-like whorls: a study of 17 cases of a distinctive histological pattern associated with dedifferentiated liposarcoma. Histopathology. 1998;33:414-424.

[8.] Yamamoto M. Electron microscopic studies on the innervation of the smooth muscle and the interstitial cell of Cajal in the small intestine of the mouse and bat. Arch Histol Jpn. 1977;40:171-201.

[9.] Ghadially FN. Ultrastructural Pathology of the Cell and Matrix. 3rd ed. London, England: Butterworths; 1988:450-453, 1234-1238.

Accepted for publication September 28, 2000.

From the Second Department of Pathology, Kinki University School of Medicine, Osaka-Sayama, Japan (Drs Yoneda, Hiruma, Satou, and Hashimoto); and Department of Clinical Pathology, Wakakusa First Hospital, Osaka, Japan (Dr Teramura).

Presented at the Second Meeting of the Japanese, Korean, Australasian, and Hong Kong Divisions of the International Academy of Pathology and Pathology Associations, Seoul, Korea, October 14-16, 1999.

Reprints: En Yoneda, MD, Second Department of Pathology, Kinki University School of Medicine, 377-2, Ohno-Higashi, Osaka-Sayama, Osaka 589-8511, Japan (e-mail: [e-mail]).