Which condition is marked by neoplastic transformation in fibrous tissue?

Fibrosarcoma is characterized by neoplastic transformation in fibrous tissue, which relates specifically to the abnormal growth of cells within the fibrous connective tissue. This malignant tumor arises from fibroblasts—cells that typically produce collagen and other fibers in connective tissue. In fibrosarcoma, however, these cells undergo changes that lead to uncontrolled proliferation, resulting in a cancerous tumor. This condition can occur in various parts of the body, including the arms and legs, but it most commonly occurs in the deep tissues of the extremities.

In contrast, other conditions listed do not involve neoplastic changes in fibrous tissue. Aneurysms pertain to the abnormal dilation of blood vessels, endocarditis is an inflammation of the inner layer of the heart, and leukemia is a cancer of the blood-forming tissues, particularly affecting white blood cells. Each of these involves different pathophysiological processes that do not align with the characteristics of fibrous tissue neoplasia.