Background: Carcinoma of unknown primary origin comprises various malignancies usually detected by tissue specific genes through
immunohistochemistry.

Aims and objectives:

1. To study the role of immunohistochemistry in diagnosing carcinoma of unknown origin.

2. Classifying malignant neoplasms of unknown origin.

Materials and methods: A cross- sectional study will be conducted in histological diagnosed cases of unknown primary in department of pathology ASRAMS from year 2023 to 2025. Haematoxylin and eosin and immune stained slides will be reviewed and classified into the main histologic types of CUP. Data will be analysed by SPSS.

Results: Out of total number of cases, the common age group of presentation (%), with sex predominance (%). The most common site/organ (%) and most common malignancy (%) , followed by other types (%). The origin remains unknown.

Conclusions: CUP cases during the study period are infrequent and primary origin of the neoplasm could be determined by immunohistochemistry. The common histological type and site can be determined.

Keywords: Unknown, Primary, Neoplasm