UESL is a rare mesenchymal tumor that predominantly occurs in children aged 6 to 10 years [
3]. However, the literature also describes isolated cases in which adults were affected by this neoplasia. Patients usually experience non-specific gastrointestinal symptoms such as abdominal pain, nausea, and vomiting. In some cases, weight loss as well as a palpable tumor in the upper abdomen are described [
4‐
6]. In addition, the radiological properties of a UESL are rather unspecific. Computed tomography typically reveals a well-defined, unifocal hepatic lesion with a cystic component that represents areas of necrosis and hemorrhages [
7,
8]. In MRI studies, UESL are predominantly described as inhomogeneous T1-hypo- and T2-hyperintensity lesions with cystic parts [
4,
7]. The interaction of missing clinical symptoms and unspecific radiological characteristics contributes to the fact that most patients are diagnosed late so the tumors are already very large at the time of diagnosis. Gabor et al. [
7] described a case series of 15 patients with UESL with a mean tumor diameter of 13.5 cm and rapid growth in 2 of these patients. In our case, the tumor showed a size increase of approx. 1.3 cm within 18 days, so that here, too, rapid tumor growth can be assumed. Some case reports describe tumors measuring up to 25 × 19 × 14 cm [
5], and there are case reports in which the patients became clinically conspicuous only after the tumor had ruptured [
9‐
11]. Due to the pronounced paraneoplastic syndrome in this case, the patient became clinically noticeable relatively early, so that the diagnosis could be made at a comparatively small tumor diameter of 5.3 × 6 cm.
The term paraneoplastic syndrome (PNS) refers to the symptoms of patients with malignant neoplasms that are due to damage to organs or tissues at sites remote from neoplasms [
12]. They can affect various organ systems, including the hematological system [
2]. In our case, in addition to typical B symptoms (fatigue, night sweats, weight loss), the patient showed pronounced leukocytosis up to 100,370/μl and increase in immature granulocytes (4.3%; norm ≤ 0.6%). Reactive leukocytosis with a white blood cell count exceeding 50,000/μl and increased neutrophilic precursors is defined as leukemoid reaction (LR) [
13], so that in the present case a paraneoplastic leukemoid reaction can be presumed. Interestingly, all paraneoplastic symptoms as well as the conspicuous laboratory parameters normalized immediately after resection of the UESL. There is another case report in the literature of a 9-year-old girl with UESL in which tumor resection also resulted in the rapid resolution of the PNS. In her case, however, the PNS consisted of a refractory long QTc syndrome, torsade de pointe, fever of unknown origin, and secretory diarrhea [
12].
Extreme leukocytosis in the form of a paraneoplastic leukemoid reaction (PLR) is a very rare disease. Granger et al. report that of 758 patients with solid tumors and extreme leukocytosis, only 77 (10%) had PLR. According to Granger, the prognosis of patients with PLR is poor and 78% of patients died within 12 weeks after the first evidence of hyperleukocytosis. Only 10% of patients survived the malignancy for more than 1 year after successful treatment of the underlying malignancy [
14]. The patient we report on is, 1 year after therapy, still alive and showed no signs of recurrence in the follow-up examinations.