An unusual case of Aβ2M amyloid deposition in bladder cancer in a non-dialysis patient.

β2-microglobulin-related (Aβ2M) amyloidosis (dialysis-associated amyloidosis) is a common complication in long-term dialysis patients. An increased concentration of β2-microgloblin (β2-m) in the serum appears to be a prerequisite for Aβ2M amyloidosis, in turn causing Aβ2M amyloid deposition predominantly in the osteoarticular tissue. There are few reports, however, of Aβ2M amyloid deposition in non-dialysis patients. We describe an atypical case of a non-dialysis patient with Aβ2M amyloid deposition in bladder cancer. A Japanese man in his 80s with no history of dialysis was admitted for transurethral resection of bladder cancer. Histopathological analysis revealed a small amount of amyloid deposition in the small-vessel wall of both the peripheral urothelial carcinoma and necrotic area. Amyloid typing by immunohistochemistry was strongly positive for anti-β2-m antibody, and β2-m was most frequently detected in laser microdissection-liquid chromatography tandem mass spectrometry. Although Aβ2M amyloidosis was expected, contrary to this, the patient's serum β2-m was only 4 mg/L, although his urine β2-m level was increased at 1340 mg/L. The unique findings observed in our patient may contribute to the elucidation of the novel pathogenesis of Aβ2M amyloid fibril formation that is distinct from conventional Aβ2M amyloidosis.