A 68-year-old female patient with clinically stable antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) with autoantibodies against myeloperoxidase (MPO) experienced a progressive increase in serum MPO-ANCA antibody titers without evidence of relapse of vasculitis.

The case report was published in a letter to the editor of Clinical and Experimental Nephrology Case Reports.

“The present case highlights the importance of using clinical judgment when considering augmenting immunosuppressive treatment in parallel with vasculitis activity. It also emphasizes the importance of searching for subclinical malignancy when the serum MPO-ANCA antibody titers of a patient with MPO-ANCA-associated vasculitis increase without evidence of relapse of vasculitis,” the authors said.

The diagnosis of MPO-ANCA was confirmed 5 years prior to clinical admission, with the disease presenting as rapidly progressive glomerulonephritis. The patient was treated with methylprednisolone pulse therapy, followed by oral prednisolone (30 mg/day).

Read more about AAV etiology

In the years that followed, her serum MPO-ANCA antibody and C-reactive protein (CRP) levels remained within normal ranges and she had microscopic hematuria while receiving oral prednisolone (2-3 mg/day).

Six months before clinical admission, her serum MPO-ANCA titer had started to rise, while her CRP and serum creatinine remained stable. Her oral prednisolone was gradually increased to 20 mg/day to control a possible relapse of AAV.

On clinical admission, the patient had a serum MPO-ANCA antibody titer of 79 U/L, which did not decrease despite administration of rituximab. However, she showed no evidence of AAV activity.

Moreover, there were no increases in serum concentrations of CRP or creatinine, or worsening of microscopic hematuria. However, due to the fluctuating MPO-ANCA antibody titer, the clinical team decided to taper the oral prednisolone dose.

Read more about AAV treatment

During this period, the patient was diagnosed with invasive ductal carcinoma in her left breast, which was resected within 1 month of diagnosis.

“Malignancy can affect immune responses and alter production of MPO-ANCA antibody independently of vasculitis activity,” the authors explained.

Her serum MPO-ANCA antibody titer decreased after excision of the primary breast cancer, reaching a level of 7.8 U/L at 6 months after surgery, while being treated with 3 mg/day oral prednisolone, and remained within the normal range during the follow-up period. Moreover, she continued free of AAV manifestations.


Yamada S, Takesako M, Kitazono T, Nakano T. Normalization of progressive increases in serum myeloperoxidase–anti-neutrophil cytoplasmic antibody titers after breast cancer resection in a patient with clinically stable microscopic polyangiitis. CEN Case Reports. Published online May 11, 2023. doi:10.1007/s13730-023-00793-8