The composite tumors of the liver are very rare, including the coexistence of HCC (hepatocellular carcinoma) with NEC (neuroendocrine carcinoma). The rare occurrence of these tumors necessitates more reported cases in order to fully understand their clinical characteristics, behaviors and treatments. Herein is described an incidental collision tumor of HCC-NEC, along with a review of the literature focusing on their clinicopathological findings and prognosis. The tumor presented here was found incidentally in the hepatectomy specimen of a 56-year-old man who had undergone liver transplantation for rapidly progressive liver failure because of alcoholic hepatitis and cirrhosis. Imaging and laboratory examinations did not demonstrate tumor-related findings. During macroscopic examination, two sharply defined and distinctive areas (1.7 cm and 0.6 cm dimension respectively) were detected among the cirrhotic nodules. The characteristic histopathological features and immunohistochemical findings allowed a diagnosis of HCC-NEC to be made. There was no evidence of recurrence and metastasis after 10 months following surgery. The present case and review revealed that these tumors are frequently found in older ages and males. Although serum markers are valuable in the discrimination of malignant tumors, their absence cannot completely rule out composite HCC-NEC. Diagnosis requires a comprehensive histopathological evaluation together with immunohistochemistry. The NEC component might influence the treatment strategy and eventually the outcome of the patient. In conclusion, the rare occurrence of HCC-NEC and the lack of diagnostic clinical signs and symptoms do not exclude their consideration in the differential diagnosis of liver tumors, especially in patients with the chronic liver disease.

ÖZET Amaç: Müllerian diferansiyasyon gösteren mediastinal kist, primer konjenital mediastinal kistler içinde nadir izlenen bir antitedir. Arka mediasten yerleşimlidir. İlk defa 2005 yılında Hattori tarafından tanımlanmış ve Hattori kisti olarak da isimlendirilmiştir. Tanı, histolojik olarak müllerian farklılaşma gösteren silyalı epitel varlığı ile konulur. Tipik olarak kist epiteli ER, PR, PAX8 ve WT-1 ile, kist duvarını oluşturan stroma α α-düz kas aktin (α αSMA) ile pozitiftir.Olgu: Olgumuz 42 yaşında, paravertebral yerleşimli, ER, PR ve WT-1 pozitif epitele sahip müllerian orijinli kistik lezyonla başvuran ve Hattori Kisti tanısı almış kadın hastadır.Sonuç: Olgu, diğer mediastinal kistlerin ayırıcı tanısında akılda tutulması gereken nadir bir antite olması nedeniyle sunulmuştur. ABSTRACTAim: Mediastinal cyst with mullerian differentiation is a rare entity among primary congenital mediastinal cysts. This cyst is located in the posterior mediastinum. It was first described by Hattori in 2005 and named as Hattori cyst. Histopathologically, diagnosis is based on the presence of ciliated epithelium with mullerian differentiation. Typically, the cyst epithelium is positive with ER, PR, PAX8 and WT-1, and the stroma constituting the cyst wall is positive with α α-smooth muscle actin (α α SMA).Case: Herein, we presented a 42-year-old female patient with paravertebral cystic lesion who was diagnosed as Hattori Cyst due to the mullerian origin of epithelium which was positive with ER, PR and WT-1. Conclusion:The case is presented because of being a rare entity that should be kept in mind in the differential diagnosis of other mediastinal cysts.Daha önce 27-30 Ekim 2018 tarihinde, Ankara'da yapılan 28. Ulusal Patoloji Kongresi'nde "poster sunumu" olarak sunulmuştur.