Correspondence Address:
Manoj Kumar Choudhuri
Department of Pathology, BS Medical College, Bankura, West Bengal
India

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Depending on existing knowledge, classification of any disease changes from time to time, as is the case with soft tissue tumors. The WHO classification of soft tissue tumors was first published in 1969 and was revised twice in 1994 and 2002.

Following are some of the major changes that have taken place in the latest classification: [1],[2]

Fibroblastic tumor / so-called fibrohistiocytic tumor : The most striking change in this group is that malignant fibrous histiocytoma has lost its glory and has been relegated to an "undifferentiated pleomorphic sarcoma." Myxoid fibrous histiocytoma has been replaced with "myxofibrosarcoma," which represents the most common soft tissue sarcoma in elderly individuals.

Smooth muscle tumor and skeletal muscle tumors : There has been no significant change in this group.

Adipocytic tumors : A well differentiated liposarcoma has no malignant potential, thus, "atypical lipomatous tumor" is the preferred term when the tumors arise at extremities and other surgically amenable sites. However, the term, "well differentiated liposarcoma" is reserved for tumors arising in the retroperitoneum and mediastinum. Incomplete resection results in local recurrence even in the absence of dedifferentiation. Myolipoma and chondroid lipoma are two new entities included in the recent classification.

Pericytic tumors : Some tumors previously categorized as hemangiopericytomas are indistinguishable from "solitary fibrous tumors." However, sinonasal hemangiopericytomas appear to be truly pericytic lesions. Large groups of pericytic / perivascular tumors have been renamed as "myopericytomas".

Vascular tumors : Spindle cell haemangioendotheliomas have been renamed as "spindle cell hemangiomas."

All of us appreciate that diagnosis by fine needle aspiration depends on pattern recognition. Thus, cytological classification of soft tissue tumors is based on the principal pattern. Immunocytochemistry has been increasingly used in the recent past for further categorization of the lesions.

Soft tissue tumors are classified into five groups [3] on the basis of their cytological results:

Pleomorphic pattern : The aspirate is richly cellular and there is a marked variation in cell size and shape. Nuclear pleomorphism is striking and some of the tumor cells show large nucleoli; bizzare tumor giant cells can be detected. Pleomorphic liposarcomas, pleomorphic undifferentiated sarcomas, and pleomorphic rhabdomyosarcomas belong to this group.

Spindle cell pattern : Spindle cells are shed as fascicles. A typical spindle cell has fusiform or ovoid nuclei; the cytoplasm is tapered, unipolar, or bipolar; mitotic figures are variable. Fibrosarcomas and leiomyosarcomas present with this classical spindle cell pattern.

Myxoid pattern : Smears show myxoid background and the matrix stains blue or blue violet in May-Grünwald-Giemsa and faintly green in Papanicolaou stain. The tumor cells could be round, spindle-shaped, or pleomorphic. Myxofibrosarcomas and myxoid liposarcomas are two common tumors encountered in this group.

Small round cell pattern : Tumor cells are individually dispersed or appear as loose, cohesive clusters of small round cells. They have round to oval nuclei and scanty cytoplasm. Ewing's sarcoma / PNET and neuroblastomas follow this pattern.

Epithelioid (polygonal) cell pattern : Tumor cells occur in groups, tight clusters, or are dispersed as round to polygonal cells with abundant cytoplasm. Epithelioid sarcomas and clear cell sarcomas show this pattern.

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