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.

This report describes a rare case of primary rectal mature teratoma in a 56-year-old woman. She was referred to the outpatient clinic with a large pedunculated rectal mass, which was found during a regular health check-up. Polypectomy was performed and microscopic findings showed various structures derived from all three germ cell layers. Epidermis, hair follicles, sebaceous glands, eccrine glands, and apocrine sweat glands, with some scattered melanophages and lymphocytes were present as ectodermal derivatives. Smooth muscle fibers, blood vessels, and fibrous and adipose tissues were found as mesodermal derivatives. In addition, thyroid follicles, mucinous glands, and bronchial respiratory epithelium with peribronchial glands were detected as endodermal derivatives. She is healthy and has shown no evidence of recurrence or distant metastasis for 25 months post-surgical resection. Primary rectal teratomas are generally benign and primarily affect women. Therefore, minimally invasive surgical procedures, such as endoscopic polypectomy for a pedunculated polyp and segmentectomy for a larger mass, are satisfactory in most cases. Induction of primary rectal teratomas has been suggested to occur mainly by errors in a single germ cell after the end of meiosis I; in addition, it has also been suggested that the difference in gender incidence may be associated with differences in sex chromosomes between males and females rather than with anatomical proximity between ovary and rectum.

A 11-year, 9-month-old female Shih-tzu was referred for evaluation of the body conditions. According to the physical examination and ultrasonography, the left ovarian mass was detected. For the removal of ovarian mass, an ovariohysterectomy was performed. Grossly, the ovarian mass was full of hairmatrix on the cut surface of the mass. Histopathological findings revealed a characteristic of teratoma, such as laminated keratines, hair, sebaceous glands, neuron tissue, differentiated bone and cartilage. The ovarian mass was well-differentiated components of 2 germ layers, and diagnosed as a mature teratoma.

Malignant transformation of mature cystic teratoma (MCT) is rare. Sarcomatoid carcinoma is a neoplasm comprising malignant mesenchymal cells and a conventional carcinomatous area. Here, we report on a case of sarcomatoid carcinoma arising from an MCT in the left ovary of a 45-year-old female. A unilocular cyst consistent with MCT was observed; however, a nodule within the cyst was confirmed from the resected ovary. Microscopically, the nodule showed both squamous cell carcinoma and pleomorphic sarcomatous components admixing with each other. Lining epithelial cells at the periphery of the main tumor showed squamous metaplasia. When a sarcomatous component is observed in the ovary tumor, it is important to find a squamous cell component, either benign or malignant.