Tumoral presentation of amyloidosis (amyloidomas) in soft tissues. A report of 14 cases.

Amyloidosis in its diverse types (immunocytic dyscrasia-associated, reactive, or heredofamilial) most often presents in a systemic form. Localized amyloidosis is uncommon in general and is exceedingly rare in the soft tissues. The authors discuss the cases of 14 patients in whom amyloidosis manifested as a localized mass ("amyloidoma") in the soft tissues (mostly mediastinal and retroperitoneal), leading to a clinical diagnosis of neoplasm in most cases. On the basis of the associated morphologically atypical and phenotypically monoclonal cell population, the resistance to potassium permanganate pretreatment, and the lack of reactivity with anti-AA antisera, 10 cases could be classified as immunocytic dyscrasia-associated AL-amyloidosis. However, four cases had histopathologic and histo- and immunohistochemical characteristics of reactive ("secondary") AA-amyloidosis. This proportion (28.5%) was higher than that suggested by the sporadic AA-amyloidomas reported in the literature. The pathologic distinction between these two categories is important because patients with AA-amyloidomas of the soft tissues appear to have a better prognosis.