Challenges in diagnosing common tumors at uncommon sites.

Rare tumors are a heterogeneous group of neoplasms with low incidence and are usually difficult to diagnose. Certain tumors that are common at specific anatomical locations rarely occur at unexpected locations and cause diagnostic challenges. Although histopathology is central to the diagnosis of these lesions, as with any tumor, ancillary techniques such as immunohistochemistry and molecular studies are often essential. In addition, a multidisciplinary approach that includes clinical, radiological, and biochemical inputs plays an important role in achieving an accurate diagnosis. A total number of 10 benign and malignant neoplastic lesions at rare locations were analyzed. Immunohistochemistry was performed for the required cases. The 10 cases included were: primary nasal meningioma, malignant melanoma of the lacrimal sac, metastatic synovial sarcoma of the thyroid, malignant teratoma of the thyroid, papillary serous cystadenocarcinoma of the paratestis, leiomyoma of the testis, squamous cell carcinoma arising in an epidermoid cyst, intraarticular synovial sarcoma of the knee, Ewing sarcoma of the kidney, and primary plasmacytoma of the breast. Knowledge and awareness of these entities improve the quality of reporting in any individual case. As a group, these lesions require further studies to enhance the understanding of their pathogenesis and patient care.