Introduction: Immunohistochemistry is a widely used diagnostic technique in pathology, the antibodies used for unvailing a tissue’s origin being made up of proteins, more specifically aminoacids. Malignant peripheral nerve sheath tumors have a distinct immunohistochemistry profile, with great emphasis concerning those with rhabdomyoblastic differentiation being positive for S-100 protein, myogenin, vimentin, CD99, p63, GFAP, caldesmon, desmin, and p53 and Myo-D1 (the later two revealing the striated muscle differentiation). Materials and methods: A case study concerning a patient suffering from a moderately differentiated (G2) non-keratinizing squamous cell carcinoma of the lung highlighted the development of an ndifferentiated sarcomatous proliferation on the left hemithorax, 7 years after the initial external radiotherapy treatment for the malignant lung tumor. Results: The immunohistochemistry analysis of the thoracic wall invasive tumor revealed it to be a malignant peripheal nerve sheath tumor with rhabdomyoblastic differentiation (Triton tumor) with the positivity for the specific aforementioned markers and a proliferation index – Ki67 of 90%. Chemotherapy was the elective treatment which was followed for 1 month, the patient having a rapid downward evolution towards exitus, with a 33 month post-diagnosis survival.
Conclusions: This case was presented due to the rarity and difficulty of the diagnosis, consisting of a rare subtype of malignant peripheral nerve sheath tumor for which there is no therapeutic consensus and with an un-favorable prognosis.