Abstract
Factor XIII deficiency is a rare bleeding disorder, which may be congenital or acquired, and is most commonly diagnosed in early childhood. It has a prevalence that is as low as one in 5,000,000. Acquired factor XIII deficiency is considered to be a more rare form, with less than 100 cases reported in the literature. This disorder can be clinically characterized by recurrent and severe unexplained bleeding. This case describes a patient with no prior bleeding disorders, who suffered from recurrent bleeding episodes while being treated with cancer immunotherapy, specifically pembrolizumab, and was subsequently diagnosed with factor XIII deficiency. She required cryoprecipitate infusion due to the persistent bleeding and subsequently developed saddle pulmonary embolism. The patient was not a candidate for tissue plasminogen activator (tPA) due to her recurrent bleeding and required mechanical thrombectomy. Given the timeline of symptoms, the patient likely developed acquired factor XIII deficiency due to her cancer immunotherapy.