Collision tumors represent occurrence of two histologically distinct tumors adjacently in the same organ without any admixture. The simultaneous occurrence of a serous adenocarcinoma with a mature teratoma is very rare. In this case report, we describe a rare case of bilateral serous adenocarcinoma of the ovary with bilateral mature teratoma and serous tubal intraepithelial carcinoma of the fallopian tube. *Corresponding author: Dr Pranab Dey, MD, MIAC, FRCPath, Professor, Department of Cytology, Postgraduate Institute of Medical Education and Research, Chandigarh, India Phone: +91172 2744401 E-mail: email@example.com Case Report C-72 Coexisting Serous Carcinoma and Teratoma Annals of Pathology and Laboratory Medicine, Vol. 02, No. 02, April June 2015 Introduction Collision tumors represent occurrence of two histologically distinct tumors adjacently in the same organ without any admixture. Though these tumors have been described in other organs such as liver, kidney, brain, lung, stomach, esophagus and bone their occurrence in ovary is rare. Mucinous carcinoma of ovary in association with mature teratoma is very rare. Herein, we describe a case of bilateral serous adenocarcinoma of the ovary with bilateral mature teratoma and serous tubal intraepithelial carcinoma of the fallopian tube. Case Report A 50 year old female presented with history of distention of abdomen along with discomfort since 1 year. Physical examination revealed abdominal distension with abdominal tenderness. Abdominal sonography revealed solid Cysts bilateral adnexal masses with moderate ascites. Her serum CA125 level was high >1000IU/ml (normal 0-35IU/ml). A diagnostic ascitic fluid tap was performed and subjected for analysis. Ascitic fluid cytology revealed tumor cells in sheets and 3D clusters favoring a diagnosis of metastatic adenocarcinoma. A preoperative diagnosis of bilateral ovarian carcinoma was made and an exploratory laparotomy with total abdominal hysterectomy and bilateral salpingooophorectomy, with omentectomy was performed. Grossly, uterus with cervix was measuring 7x4x3cms, cut surface was unremarkable. Both ovaries were grossly replaced by tumor with multiple areas of capsular breach and surface nodular deposits on both sides. Right ovary was enlarged and measured 8x6x5cms (figure 1a), cut surface showed soft to firm tumor with focal cystic degeneration and areas of haemorrhage and necrosis (figure 1b). Capsule showed numerous deposits with papillary excrescences. Right ovary also showed a cystic area filled with mucoidy material measuring 2x1.5 cm along with cartilaginous areas. Left ovary was cystically enlarged and showed cystic filled with cheesy material. Bilateral fallopian tubes showed surface nodules. Omentum showed multiple tumor deposits ranging in size from 0.5 to 3 cm. Microscopic examination of the right ovary revealed a cyst lined by pseudostratified ciliated columnar lining epithelium along with mucinous glands and cartilage. The adjoining areas showed high grade serous adenocarcinoma in the form of papillae; glands and solid sheets of tumor cells with moderately pleomorphic vesicular nuclei, conspicuous nucleoli and moderate cytoplasm (figure 2a. b). The left ovary revealed a cyst lined by stratified squamous epithelium and filled with keratin flakes. The adjacent areas showed high grade serous adenocarcinoma. Bilateral fallopian tubes also showed high grade serous adenocarcinoma along with serous tubal intraepithelial carcinoma (figure 2c) which was better highlighted on immunostaining with p53 which showed nuclear positivity (figure 3a) along with a high Ki 67 index (figure 3b). Fig. 1a: Gross photograph of uterus, cervix with bilateral ovaries and fallopian tubes. Bothe the ovaries are enlarged and replaced by a tumor. Fig. 1b: Cut surface of the ovary showing a tumor with a variegated appearance with solid areas, cystic areas and cartilage.