MO108: Paraneoplastic Nephrotic Syndrome in a Man with Breast Cancer

Abstract BACKGROUND Nephrotic syndrome is associated with many solid tumours and haematologic malignancies. Membranous nephropathy (MN) is the most commonly reported paraneoplastic glomerulonephritis; about 10% (rate 5–20%) of adults with MN have been reported to have a malignancy [1]. Less frequently, minimal change disease, focal segmental glomerular sclerosis, membranoproliferative and crescentic glomerulonephritis, IgA nephropathy [1] and thrombotic microangiopathy [2] have been associated with cancer. Differentiating primary from secondary glomerular disease in patients with malignancy can be difficult. The probability of a secondary form is higher when the appearance of proteinuria or nephrotic syndrome precedes by few months or develops within a year of cancer diagnosis. The suspicion of paraneoplastic nephropathy is even stronger when tumour remission is associated by significant fall in proteinuria and when recurrence of malignancy is followed by the development of clinical glomerular disease. Solid tumour most commonly associated with glomerular diseases (mainly MN) is lung cancer, followed by prostate and colorectal cancer. Paraneoplastic glomerular diseases are rarely linked to breast cancer. In two reviews, breast cancer was reported only in 3% (5 out of 159 patients) [1] and 8% (6 out of 85 patients) of patients with MN and solid tumours. Breast cancer is the most common malignancy in women, while it is a rare disease in men. Male breast cancers account for less than 1% of all diagnosed cases, and the mean age is usually over 60 years [1]. METHODS We report the case of a breast cancer in a man associated with a paraneoplastic nephrotic syndrome. A 76-year-old man was managed at our renal department since 2016 for chronic kidney disease. He was overweight and affected by non-insulin dependent diabetes mellitus, arterial hypertension and coronary artery disease. Since 2016 to December 2020, he had stable renal function with serum creatinine levels ranging from 2.5 to 3.0 mg/dL and a normal urinary protein excretion rate (100–150 mg/24 h). In March 2021, the patient developed a right periareolar breast swelling, pain and erythema with yellowish nipple discharge. In the same period, a full-blown nephrotic syndrome with heavy proteinuria (8 g/24 h) was observed, and serum creatinine increased to 3.5–4.0 mg/dL. Immunological blood tests were negative, including anti-PLA2R and anti-THSD7A antibodies. A kidney biopsy could not be performed due to bilateral renal cysts. Mammogram examination and ultrasound imaging revealed ductal ectasia and microscopic calcifications at the site of right breast lesion, so a diagnosis of cancer was made. RESULTS In September 2021, the patient underwent radical right mastectomy and histopathological examination confirmed early-stage breast cancer (pT1a, pN0, Mx R0, ER 100%, PgR 0, Ki67 5%, CerbB2 neg). In the following month, the 24-h urinary protein excretion markedly reduced to 1.4 g and the nephrotic syndrome resolved completely, confirming its secondary origin. CONCLUSIONS Paraneoplastic nephrotic syndrome is a rare complication of cancer. Its recognition and detection of an undiagnosed malignancy could be life-saving. To our knowledge, this is the first case reported in literature of paraneoplastic nephrotic syndrome in a man affected by breast cancer.