The agent is used in several animal species, that is, dogs, cats, rabbits, rats, horses, sheep, and cattle. Table 1 at Fenbendazole is widely used as an antiparasitic agent against various gastrointestinal parasites, such as pinworms, giardia, roundworms, hookworms, Taenia solium, and pulmonary paragonimiasis.

The result was 6 points, indicating a “probable” adverse reaction to fenbendazole (see online suppl. The causality assessment evaluation was performed by using the Nranjo Adverse Drug Reaction Probability Scale. Her AST, ALT, and total bilirubin levels had normalized on September 30, and on November 25, 2019, pembrolizumab monotherapy was terminated due to increased tumor size in the right upper lobe of her lung. Her CEA levels rose slightly after starting fenbendazole (i.e., 52.7–76.7 ng/mL), and a CT scan on August 15 showed no change in tumor size (Fig. Subsequently, pembrolizumab was recommenced, and there was no relapse in liver dysfunction. We stopped fenbendazole administration immediately, and her liver function parameters gradually improved. She stated her fenbendazole schedule consisted of 1 g/day PO for 3 days, followed by 4 days off, and this schedule had been maintained for approximately 1 month from early July until her August visit. She had purchased and started taking oral fenbendazole, which was marketed as an anthelmintic for dogs, based on information from social media sites stating it was effective against cancer. She and her family had become afraid of cancer progression since her CEA levels had increased. For this reason, pembrolizumab monotherapy was temporarily discontinued, but after interviews with her family, it was discovered she had been taking oral fenbendazole since early July 2019. Initially, we suspected liver injury as an immune-related adverse event. She had no known history of drug or food allergies. Her physical findings and vital signs were unremarkable. Therefore, the patient was admitted to our hospital on an emergency basis (Fig. When she was next seen on August 13, 2019, blood tests showed elevated aspartate transaminase (AST) levels at 386 U/L, alanine aminotransferase (ALT) at 487 U/L, and total bilirubin at 1.3 mg/dL, although her liver function 3 weeks ago was at the upper limit of normal (ULN), with an AST level of 24 U/L (ULN ≤33 U/L), ALT of 16 U/L (ULN ≤27 U/L), and total bilirubin of 0.8 mg/dL (ULN ≤1.2 mg/dL).

In February 2019, CEA levels began to increase however, a CT scan showed stable disease, and treatment with pembrolizumab monotherapy was continued. Three months later, a CT scan showed a partial tumor response and decreased carcinoembryonic antigen (CEA) levels. In November 2018, we initiated PD-1 inhibitor treatment, that is, pembrolizumab monotherapy. Sequent analyses and the programmed death-ligand 1 (PD-L1) IHC 22C3 pharmDx assay (Dako North America) revealed the tumor had a KRAS G12A mutation, and PD-L1 expression as evaluated by the tumor proportion score was 80%. She had stage IVB (cT4N2M1c) with brain metastases. She underwent a transbronchial lung biopsy and was diagnosed with lung adenocarcinoma. In October 2018, an 80-year-old woman was admitted to Aichi Cancer Center Hospital with a tumor in the upper lobe of her right lung. Physicians should enquire patients about self-administration of orally ingested products, including dietary supplements, herbs, or bioactive compounds, in cases of unexpected adverse reactions. However, sources of medical information on these platforms are often unproven, and it is difficult for nonmedical professionals to accurately select and filter complex medical information. Twitter and Facebook are online social media platforms which have been constructively used to exchange information among cancer patients. This is the first case report of a patient with advanced NSCLC who self-administered the anthelmintic, fenbendazole.

The antitumor inhibitory effects of fenbendazole have been reported however, she did not experience tumor shrinkage. After discontinuation of the self-administration of fenbendazole, the patient’s liver dysfunction spontaneously resolved. An interview with her and her family revealed that she had been taking fenbendazole for a month, solely based on social media reports suggesting its effectiveness against cancer. The patient experienced severe liver injury 9 months later. An 80-year-old female patient with advanced nonsmall cell lung cancer (NSCLC) was started on pembrolizumab monotherapy. The agent is also reported to exert antitumor effects and inhibit microtubule-associated tubulin polymerization, but its safety and tolerability profile in humans remains unclear. Fenbendazole is a benzimidazole anthelmintic agent, with a broad antiparasitic range in animals such as dogs and pigs.

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