BACKGROUND: Nephrotic syndrome (NS) can occur as a paraneoplastic disorder in association with various types of carcinoma. However, paraneoplastic nephrotic syndrome (PNS) is often misdiagnosed as idiopathic nephrotic syndrome or as an adverse effect of oncology treatment, leading to delayed diagnosis and suboptimal treatment. The characteristics of NS associated with solid malignancies are not yet elucidated. We systematically summarized the clinical data for 128 cases of NS combined with solid malignancies with the aim of informing the clinical management of PNS.
METHODS: We searched the PubMed database for articles published from the date of inception through to October 2023 using the following keywords: \"cancer\" or \"malignant neoplasms\" or \"neoplasia\" or \"tumors\" and \"nephrotic syndrome\", \"nephrotic\" or \"syndrome, nephrotic\". All data were extracted from case reports and case series, and the extraction included a method for identifying individual-level patient data.
RESULTS: A literature search yielded 105 cases of PNS and 23 of NS induced by cancer therapy. The median age at diagnosis was 60 years, with a male to female ratio of 1.8:1. In patients with PNS, manifestations of NS occurred before, concomitantly with, or after diagnosis of the tumor (in 36%, 30%, and 34% of cases, respectively). Membranous nephropathy (49%) was the most prevalent renal pathology and found particularly in patients with lung, colorectal, or breast carcinoma. Regardless of whether treatment was for cancer alone or in combination with NS, the likelihood of remission was high.
CONCLUSIONS: The pathological type of NS may be associated with specific malignancies in patients with PNS. Prompt identification of PNS coupled with suitable therapeutic intervention has a significant impact on the outcome for patients.

Paraneoplastic syndromes are immune disorders associated with clinical signs and symptoms caused by substances produced by malignant diseases and are not directly associated with a primary or metastatic tumour. The symptoms are the effects of hormones, immune cross-reactivity or cytokines. Paraneoplastic nephrotic syndrome (PNS) is often associated with membranous nephropathy (MN) in elderly patients with solid tumours, and there is continued debate regarding whether corticosteroids or immunosuppressants should be combined with cancer therapy for the syndrome. The present report describes a male patient with lung cancer associated with secondary MN who achieved remission under radiotherapy, with no use of corticosteroids or immunosuppressants. This case is rare. Therefore, when treating PNS related to lung cancer, more attention should be paid to the treatment of the cancer.

Paraneoplastic nephrotic syndrome is often a complication in patients with cancer, and various histologic lesions have been described in the kidney. We report the case of a 76-year-old woman who presented with a podocytopathy that was found to be associated with a small cell lung carcinoma (SCLC). One cycle of carboplatin-etoposide combination therapy led to resolution of nephrotic syndrome and remission of the lung carcinoma. C-Maf-inducing protein (C-Mip) was overexpressed in both podocytes and cancer cells, but was not found in control kidney and lung tissue samples. C-Mip also was absent in SCLC cells from 30 patients without nephrotic syndrome. Exposing cultured podocytes to a sample of our patient\'s serum that was collected prior to chemotherapy led to disorganization of the podocyte cytoskeleton and induction of C-Mip expression, which was not observed with control serum or our patient\'s serum sampled after chemotherapy. These observations suggest that C-Mip may play an important role in SCLC-related podocytopathy and that a circulating factor likely induces its expression in the kidney.

A 58-year-old man presented with recurrent frontal meningioma and nephrotic syndrome. Renal biopsy could not be done in view of the rapid neurological deterioration. The patient underwent surgical resection of the tumor. Within 4 weeks, the edema decreased, serum albumin improved, and proteinuria decreased spontaneously. At three months of followup, the patient had attained complete remission of nephrotic state.