A 52-year-old male patient presented in the emergency department with fatigue and persistent back and flank pain. Computed tomography revealed lymphadenopathy and disseminated osseous lesions. Staging was completed and a low differentiated signet ring cell carcinoma of the distal esophagus (AEG I), UICC stage IV [1], was diagnosed. Immunohistochemistry showed expression of human epidermal growth factor receptor 2 (HER2)/neu and E-cadherin without expression of programmed death-ligand [1]. No microsatellite instability was detected. Palliative polychemotherapy with 5-fluorouracil, folinic acid, oxaliplatin and docetaxel (FLOT) was initiated. Due to progressive pancytopenia with transfusion-dependent thrombocytopenia, abnormal renal function tests, fever and rapid clinical deterioration, we suspected malignancy-associated Thrombotic Microangiopathy (TMA), and therefore promptly initiated daily plasmapheresis. However, no objective response upon plasmapheresis was observed, while extended laboratory tests revealed elevated levels of lactate dehydrogenase (1477U/l, range: 135-250U/l), ferritin (4410µg/l, range 30-400µg/l), triglycerides (366mg/dl, range >200mg/dl) and soluble interleukin 1 receptor (1807IU/ml, range: <710IU/ml). Abdominal ultrasonography revealed splenomegaly. Notably, bone marrow biopsy revealed extensive carcinomatosis and activation of stromal macrophages (Figure 1). According to those findings and a calculated H-score (reference: http://saintantoine.aphp.fr/score/), malignancy associated Secondary Hemophagocytic Lymphohistiocytosis (sHLH) was diagnosed. Thus, we initiated treatment with interleukin (IL)-1 inhibition (Anakinra), prednisolone and continuation of polychemotherapy, resulting in a significant clinical improvement and decline of ferritin (1990.4µg/l) and lactate dehydrogenase (860U/l) levels. Subsequently, the patient successfully completed six cycles of polychemotherapy but eventually died due to progressive esophageal carcinoma. What do we learn from this unusual case? First, distinguishing sHLH from TMA in the context of rapid onset thrombocytopenia along with clinical and laboratory deterioration is extremely challenging. However, extensively elevated ferritin levels are indicative for HLH and may guide diagnostic considerations early on [2]. Second, Bone Marrow Carcinomatosis (BMC) due to gastric or esophageal carcinoma is a highly rare event [3,4], and concomitant sHLH is a yet underreported, but potentially life-threatening phenomenon in this context. HLH is a hyperinflammatory syndrome leading to an uncontrolled cytokine storm with an all-cause mortality of approximately 40% in adults [5]. Although exact path mechanisms remain unclear, dysregulation of immune homeostasis due to chemotherapy and underlying malignancy might lower the threshold for triggering sHLH [6]. However, in this patient we considered BMC as driver of sHLH and therefore decided to continue chemotherapy. Third, therapeutic decision-making remains challenging due to a lack of validated treatment protocols in a...