Testicular germ cell tumors (GCT) arise from embryonic or extraembryonic differentiated totipotential germ cells. The tumor cells can differentiate into germ cells as well as, other lineages including yolk sac tumors, choriocarcinomas, and teratomas. Mixed GCT is composed of more than one GCT component including one or more nonseminomatous elements in a tumor, accounting for one-third of GCT. Herein we report the case of a collision tumor with two distinct and separated GCTs in the testis, adjacent to each other. A 48-year-old, previously healthy man showed the hard swelling and heterogeneous enhancing mass in the right scrotum, and right orchiectomy was performed. Grossly, the lesion was two distinct and well-circumscribed masses in the testis. Microscopically, a larger tumor was immature teratoma (prepubertal type) and another smaller tumor was seminoma. These two tumors can be from a common precursor, germ cell neoplasia in situ (GCNIS); however, they are two distinct pathological entities. Given that teratomas can evolve from seminomas by additional genetic alterations, seminomas are also a precursor for postpubertal-type teratomas. Two distinct GCNISs may occur at different times. Because GCNIS is patchy distributed, a close gross examination must be performed in GCNIS or GCT to miss other GCTs with poor prognosis and to prevent under-treatment.

cording to histopathological characteristics. One is composite tumor, and the other is collision tumor. Composite tumor is a lesion showing the combined histopathological characteristics of two or more previously recognized tumor and/or cysts of different categories. Two constituent parts are mixed with each other, and histological transition is often observed. On the other hand, collision tumor is a lesion showing the independent histopathological characteristics of two or more previously recognized tumor and/or cysts of different categories. Two constituent parts are separated each other by connective tissue, and histological transition is not observed. Their origin is still unclear. In this study, a collision tumor was reported. 77-year old woman was referred to CNUH with a neck mass in right submandibular area. Incisional biopsy was carried out, and the patient was diagnosed as collision tumor of squamous cell carcinoma and neurofibroma. After reviewing studies reporting collision tumor from head and neck area, formation of a collision tumor was most frequent from a cervical area and average age is 59.6. A collision tumor commonly lead to misdiagnosis, and the prognosis is not always transparent. The variety symptom of collision tumor has to be kept in mind in the diagnosis and treatment of the lesions in head and neck area.