A 37-year-old white male presented to the Emergency Department with acute chest pain and breathlessness causing marked reduction in exercise tolerance. He denied loss of consciousness, cough, or other infective symptoms and had no symptoms of deep vein thrombosis. He did not have a personal or family history of venous thromboembolism nor any identifiable risk factors. He had been prescribed fluoxetine 60 mg once daily orally and promethazine 25 mg at night orally for low mood and insomnia and suffered mechanical back pain, but otherwise did not have any significant comorbidities. He is a non-smoker, drinks alcohol within recommended limits, denies recreational drug use, and works as a light technician. On examination, the patient was febrile (temperature 37.8 °C), hypoxic (oxygen saturation 92% on room air), tachypneic (respiratory rate 24 breaths/minute), tachycardic (heart rate 120 beats/minute), and normotensive (blood pressure 132/84 mmHg). He was alert but appeared pale, with normal heart sounds and no murmurs heard. Auscultation of the chest was normal, and his abdomen was described as soft and nontender. There were no abnormalities on neurological examination. Electrocardiography (ECG) showed sinus tachycardia, right axis deviation, ischemic changes in the anterior leads, and the S1Q3T3 phenomenon. Initial laboratory results are presented in Table. Assessment of d-dimer was not performed—we assume because clinical suspicion of VTE was sufficiently high to proceed directly to imaging and empirical treatment. Arterial blood gas sampling performed on room air revealed pO2 7.6 kPa, pCO2 7.6 kPa, hydrogen ion concentration 32 nmol/L, base excess 0.7 mmol/L, lactate 1.36 mmol/L, and oxygen saturation 92%. The patient routinely tested negative on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) polymerase chain reaction (PCR) during admission, and there was no indication for other microbiological/serological testing. The patient was treated for presumed pulmonary embolism with subcutaneous tinzaparin 17,000 IU/mL and proceeded to computed tomographic pulmonary angiography (CTPA). CTPA confirmed major pulmonary embolus, with associated acute right heart strain and dilation of the pulmonary trunk. The patient was transferred to the medical high-dependency unit for monitoring and continued treatment with tinzaparin. Echocardiogram confirmed the CTPA findings, demonstrating a dilated right heart with impaired right ventricular function and very mild tricuspid regurgitation. The doctor in training responsible for his care at this point also requested a computed tomography (CT) scan of the abdomen and pelvis routinely to screen for malignancy. CT abdomen and pelvis was also documented in the management plan by two different consultant physicians. The same doctor in training then reviewed the patient 48 hours later and documented in the case notes at that time that National Institute for Health and Care Excellence (NICE) guidance dated March 2020 stated “not to offer further investigations for malignancy in patients with unprovoked PE unless relevant clinical signs or symptoms.” Despite this, the patient proceeded to CT scan without any symptoms or signs to suggest malignancy. The rationale for proceeding to CT scan is not documented in the medical notes and will be addressed in the discussion of the case. CT revealed extensive thrombus extending from the proximal left external iliac vein into the left common iliac vein and along the inferior vena cava (IVC) to the level of the renal veins. The report also noted some prominent paraaortic nodes at the level of the renal veins and suggested these may be reactive. The solid abdominal organs appeared normal, and a small left-sided pleural effusion was noted. Due to unexplained lymphadenopathy, an astute clinician advised testicular examination. The patient did not self-examine regularly but denied testicular symptoms. Clinical examination was unremarkable, but he proceeded regardless to ultrasound examination. Ultrasound showed several hypoechoic and heterogeneous lesions identified within the right testis, the largest measuring 1.7 cm. There was some vascularity within these lesions with appearances suggestive of testicular malignancy. The testicle did, however, appear normal in size, which would support the clinical examination findings. Following discussion with the local Urology service, assessment of tumor markers was performed, which revealed elevated lactate dehydrogenase (LDH) at 449 U/L (reference range 0–250 U/L) with beta human chorionic gonadotropin (hCG) and alpha fetoprotein (AFP) within the normal range. The differential diagnosis was metastatic testicular cancer of germ cell origin or lymphoma. Tissue diagnosis would be required to confirm the diagnosis and guide treatment; however, orchidectomy was complicated by the need for anticoagulation in the context of significant thromboembolic disease. Following multidisciplinary discussion, the patient was discharged to continue anticoagulant treatment with tinzaparin with a plan for delayed orchidectomy following reduction in clot burden. On the advice of the Haematology service, tinzaparin was changed to subcutaneous enoxaparin because of subtherapeutic anti-Xa levels following discharge. The dose was adjusted on several occasions; at the time of writing, the patient continues on enoxaparin 140 mg twice daily. Other medications administered were co-codamol 30/500 orally on an as-required basis for treatment of pain, allopurinol 300 mg once daily orally to reduce risk of spontaneous tumor lysis syndrome, and the patient’s preadmission medications: fluoxetine 60 mg once daily orally and promethazine 25 mg once daily orally, all of which were continued long term. The duration of anticoagulation had not yet been determined at time of discharge, pending cancer treatment and follow-up in due course. Unfortunately, repeat imaging 20 days after presentation showed progression of the IVC thrombus and persistent pulmonary artery filling defects, corresponding to pulmonary embolism. IVC filter insertion was performed to facilitate right orchidectomy, which revealed 35-mm seminoma with invasion of the rete testis and hilar soft tissue. Orchidectomy was complicated by scrotal hematoma, which was surgically evacuated. A repeat CT scan showed that aortocaval adenopathy had increased in volume from previous scans. Following multidisciplinary discussion, the patient’s disease was staged as stage 2A seminoma and the decision taken to proceed to adjuvant radiotherapy (30 Gray in 15 fractions) which was completed in December 2020. Less than 1 month later, abdominal CT imaging was repeated to assess burden of thrombus prior to IVC filter removal. This unfortunately showed multiple pulmonary and hepatic metastases. The decision was taken to proceed with bleomycin, etoposide and platinum (cisplatin) (BEP) chemotherapy, of which the patient completed four cycles in April 2021. Repeat CT showed good response to chemotherapy, and the patient remains well. He continues on therapeutic anticoagulation with enoxaparin and awaits specialist review by Haematology services to determine the duration of treatment.