OBJECTIVETo study the clinicopathologic features of osteomalacia or rickets-associated mesenchymal tumors.

METHODSThe clinical and pathologic findings of 10 cases of osteomalacia or rickets-associated mesenchymal tumors were evaluated. Hematoxylin and eosin stain, immunohistochemistry and histochemistry were performed on the archival paraffin sections.

RESULTSAmongst the 10 patients studied, 6 were males and 4 were females. Their age at the time of operation ranged from 28 to 69 years ( mean = 45.6 years). A history of long-standing bone pain, arthralgia, limitation in movement, hypophosphatemia and hyperphosphaturia was present in all cases. The duration of symptoms ranged from 2 to 27 years (mean = 9.6 years). The tumor size ranged from 1 to 7 cm (mean size = 3.52 cm). Microscopically, the tumors were composed of various mesenchymal cells, including spindled fibroblast-like cells, adipocytes, chondroid cells and mucinous cells. The background was rich in blood vessels. In 8 of the 10 cases, there was also dystrophic calcification in an unusual flocculent or "grungy" pattern. Peripheral woven bone shell formation was noted in 2 cases and non-urate crystal deposition in 2 cases. Mitotic figures were rare in 9 cases. In 1 of the 10 cases however, mitotic figures and bizarre cells were commonly encountered. On immunohistochemical study, the tumor cells were all positive for vimentin. There was focal positivity for smooth muscle actin and CD34 in 5 and 3 cases respectively. The staining for desmin, S-100 and AE1/AE3 was negative. Ki-67 proliferation index was less than 4% in 8 cases and 30% in 1 case. Alcian blue-positive mucinous matrix and mucinous degeneration around vessels were noted in 8 cases.

CONCLUSIONSMost of the osteomalacia or rickets-associated tumors are either benign or low-grade malignant mesenchymal tumors. They can be mistaken as other neoplasms due to the morphologic heterogeneity present. Thorough understanding of the associated clinical features and laboratory investigation results is helpful in arriving at the correct diagnosis.