[A case of thrombotic microangiopathy with glomerular subendothelial IgA deposition due to bevacizumab]

Bevacizumab, an inhibitor of vascular endothelial growth factor, is approved for the treatment of various cancers, but the incidence of proteinuria as a side effect has been reported to be 2-64%. We report a case of renal impairment due to thrombotic microangiopathy (TMA) accompanied with glomerular subendothelial deposition of IgA resulting from bevacizumab administration. A 57-year-old female with advanced breast cancer, to whom bevacizumab had been administered from October 2012, developed proteinuria and epithelial casts in her urine about a month later. Serum creatinine remained at 0.7-0.8 mg/dL until June 2013, but gradually increased to 1.3 mg/dL in September. She was referred to our hospital because her renal function had not improved despite termination of bevacizumab, and a renal biopsy was performed in October. At that time, the levels of proteinuria, serum creatinine and serum IgA were high at 1.3 g/g x Cr, 1.6 mg/dL and 430 mg/dL, respectively. Histological examinations showed prominent IgA deposits in the subendothelial area and glomerular infiltration of CD68 positive cells in addition to features of TMA, such as narrowed glomerular capillary lumina and double contours of the basement membranes. In consideration of her clinical history, a diagnosis of bevacizumab-induced TMA was made. Through follow-up care without readministration of bevacizumab, epithelial casts in her urine disappeared, and proteinuria decreased to 0.62 g/g x Cr in November. Serum creatinine remains high at around 1.3 mg/dL, but has not elevated further. Serum IgA gradually decreased and reached 289 mg/dL in April 2014. TMA due to bevacizumab described in several other reports was also accompanied by glomerular IgA deposition, thus a differential diagnosis of IgA nephropathy is required. TMA was recently added to a section of "significant adverse effects" in the package insert of bevacizumab. Nephrologists should be fully aware of this drug-induced nephropathy.