An Intriguing Case of Arteriovenous Fistula Mass

Introduction: Arteriovenous (AV) fistula in kidney transplant recipients may develop complications such as thrombosis, aneurysms or infection, however cancer metastasis is a rare occurrence. Case Description: A 65-year-old female with history of kidney transplant in 2009 presented with painful hand swelling. In 2019 a chest xray showed 4.4cm left lung mass with transbronchial biopsy demonstrating non-squamous cell lung carcinoma (NSCLC), PD L1+, treated with radiation therapy. A surveillance CT scan showed a new mass in left upper lobe 3.3 x 2.9 cm with positive avidity on PET scan. Lung biopsy 08/19/2020 showed NSCLC reoccurrence, treated with radiation. A PET scan on 04/15/2021 showed a new lung mass and FDG avidity in transverse colon, however a lung biopsy was negative for malignancy on 03/09/2022. Surveillance imaging for cancer remained negative until the patient presented with right arm pain. AV fistula ligation performed on 11/18/2022. Tissue pathology revealed positive staining for CK7 and TTF-1 consistent with metastatic lung adenocarcinoma. PET scan 12/2022 demonstrated a new left lung mass with mediastinum lymph nodes along with known metastasis in right AVF. Discussion: Tacrolimus binds to FK506 binding protein-12 which causes calcineurin inhibition. Calcineurin dephosphorylates NFAT (nuclear factory of activated T cells) which oversees IL-2 production amongst other cytokines. When this downstream pathway is inhibited, T cell activation is disrupted, which is advantageous for immune suppression but can cause failure of immune checkpoint systems to detect cancerous cells [3]. Circulating tumor cells that escape immune surveillance can lodge in areas of low blood flow[1]. In this case, factors including aneurysm and thrombus formation may have contributed to metastasis seeding. This case emphasizes the need to consider metastasis in patients with a cancer history with new or enlarging vascular masses.