AB 29. Malignant mediastinal tumor: restrictions in immunohistochemical evaluation

Background: It is common ground that immmunohistochemistry’s contribution in neoplasm’s origin identification is invaluable. However, in some cases there seem to exist certain limitations raising differential diagnosis problems.
Patients and methods: A young 23-year old woman, who was recently pregnant and breastfeeding, presented to our hospital with dyspnea and superior vena cava syndrome. A month ago she suffered from upper respiratory tract infection, which was treated with antibiotics. Axial computed tomography showed several mediastinal masses and right lower lobe lung invasion. This was followed by bronchoscopy and samples were taken for biopsy.
Results: Upon histological evaluation a malignant neoplasm with extensive necrosis was revealed. Diffuse distribution of oval, middle to large size cells, with conspicious nucleoli and mitoses, tend to lead to the diagnosis of a lymphoproliferative neoplasm. During to gradual and extensive immunohistochemical examination, the neoplastic cells were found negative to stains specific for hemopoietic system diseases as well as other malignant neoplasm such as sarcoma, mesothelioma, germ cell tumor, melanoma and neuroendocrine carcinoma. On the other hand, they were strongly positive for p63 (squamous cell differentiation index), CD138 and only weak and focally for keratins (CKAE1/AE3, CK8/18, CK7, CK5/6). Morphological and immunohistochemical findings consisted with undifferentiated carcinoma, with squamous cell differentiation. The patient deceased 20 days later.
Conclusions: Neoplastic morphological features tend to lead to a correct diagnosis which should always be certified by immunohistochemical findings. However, in some cases immunohistochemistry’s role is diminished due to tumor specific factors as neoplastic cells’ poor differentiation or dedifferentiation and degenerative changes.