This Literature - Spontaneous case, initially received on 21-Dec-2016, was reported by a health professional and concerns a 55-year-old male patient. Weight: not provided; Height: not provided. At the time of the event, the patient had lung neoplasm malignant (newly diagnosed right lung cancer), anemia (grade 1), thrombocytopenia and a normal white blood cell count. Concomitant medication: not reported. Administration of company suspect drug(s): On an unknown date, the patient received Influenza Virus Vaccine (INN) for indication not reported. Dose regimen: Not reported, Route of administration: Not Reported. Batch number: Not reported. Site: Left-sided. No additional suspect drugs. Adverse reactions/events and outcomes: On an unknown date 2-3 days post vaccination, the patient experienced Systemic immune response related to influenza vaccination (medically significant, outcome: recovered). Symptoms included FDG (F-fluorodeoxyglucose)-avid left axillary lymph nodes on positron emission tomography (PET)/computed tomography (CT), intense splenic F-fluorodeoxyglucose (FDG) uptake on positron emission tomography (PET/computed tomography (CT), new enlarging FDG (F-fluorodeoxyglucose)-avid left axillary lymph nodes, a left supraventricular lymph node, FDG (F-fluorodeoxyglucose) uptake in the spleen. visualization of the systemic immune response in the spleen. Axial PET and fused PET/CT images from FDG-PET/CT examinations were performed before, 2-3 days following and 12 days following the influenza vaccination which was administered in the left upper extremity. Maximum intensity projection (MIP) images show the metabolically active right lung mass and ipsilateral hilar metastases, but also new enlarging FDG-avid left axillary lymph nodes, a left supraclavicular lymph node, and intense splenic FDG uptake compared to an FDG-PET/CT scan performed at an outside institution two months prior. The splenic uptake raised the question of a systemic inflammatory process and further questioning revealed that the patient received an influenza vaccine in the left upper extremity 2-3 days before the examination. Since contralateral metastases would alter management, FDG-PET/CT was performed 12 days later without interval therapy. Left axillary and supraclavicular nodal and splenic FDG uptake resolved. The diffuse splenic uptake of FDG on the examination 2-3 days following the influenza vaccination with a mean standardized uptake value corrected for lean body mass (SULmean) was 3.1, while that same finding is absent on the examinations prior to (SULmean, 1.3) and 12 days following the vaccination (SULmean, 1.5). Although involvement of metastatic disease is possible, the diffuse pattern and relatively lower level of FDG uptake in the spleen compared with the primary right lung cancer suggests a different etiology. A diffuse increase in bone marrow uptake of FDG typically accompanies splenic uptake due to recent administration of granulocyte colony stimulating factors, to a greater extent than what was present in our study (bone marrow SULmean prior to immunization, 1.6; 2-3 days following immunization, 1.8; 12 days following immunization, 1.4). In addition, there are a few cases reports of rare cytokine-producing lung tumors causing increased FDG uptake in bone marrow and cytokine production could also conceivably result in increased uptake in the spleen. Subsequent FDG-PET/CT scan 6 months later was negative for malignancy in the left axilla and spleen. Reporter's Comments: Reporter's assessment: A limitation of this case is lack of pathologic confirmation, however, this would have required a splenectomy.  Left axillary and supraclavicular nodal and splenic FDG uptake resolved and was presumably due to local and systemic immune-mediated responses to the vaccine. FDG uptake can be seen in lymph nodes ipsilateral to an FDG injection site, especially if tracer is extravasated. In this case, FDG was injected in the left antecubital fossa 2-3 days after vaccination, and in the right hand approximately 2 weeks later. This is a confounding factor in this case, however, the ipsilateral FDG injection alone does not explain the enlarging size of the left axillary lymph nodes, the left supraclavicular lymph node and the increased splenic uptake compared to the outside scan before vaccination. The healthcare professional stated that a simultaneous increase in metabolism in lymph nodes ipsilateral to the site of vaccine administration and the spleen should be considered in the differential diagnosis in the evaluation of patients with cancer and that a careful history, overall pattern of uptake and time course helped to avoid a false-positive interpretation for progressing lung cancer and alteration of the radiation therapy plan; Sender's Comments: Listedness: Brand of Influenza vaccine not specified. Assessment according to the CCDS for CSL's Influenza Virus Vaccine, systemic immune response is unlisted. Causality: Related. Time to event onset is 2-3 days following vaccination. Patient received influenza vaccine in left upper extremity, same side of increased uptake of axillary and supraclavicular nodes.  Other causes for increased FDG uptake (granulocyte colony stimulating factor administration, cytokine producing lung tumour) and metastatic progression of underlying lung cancer were excluded. Subsequent FDG-PET/CT scan 12 days later without treatment (for lung cancer) and 6 months later was negative for malignancy. Systemic immune response is plausible following influenza vaccination; causality is considered related due to temporal association.