Histopathological evaluation is central when cancer without known origin occur. It is a difficult task to evaluate the origin of some types of carcinoma, because they can have the same appearance despite different origin.
Distribution of histological types (2):
- Well- and moderately differentiated adenocarcinomas (50 %)
- Poorly differentiated carcinomas with or without glandular differentiation (30 %)
- Squamous cell carcinomas (5 %)
- Undifferentiated/anaplastic carcinomas (5 %)
|Photomicrograph of poorly differentiated adenocarcinoma in a lymph node. Click to enlarge.
||Photomicrograph of an adenocarcinoma in the pleura. Click to enlarge.
||Photomicrograph of undifferentiated carcinoma in a lymph node. Click to enlarge.
An extensive immunohistochemical investigation is often performed in these instances, even where specific finding indicates tumor origin.
Some immunohistochemical markers are highly specific and are thus included in most panels, such as: MelanA for malignant melanoma, PSA for prostate and thyroglobulin for thyroid. There are also combinations of markers that strongly indicate special tumor types. However, in a number of cases there are no specific findings, and it must be concluded with carcinoma of unknown origin.
Molecular techniques based on gene analysis can hopefully improve the diagnostic performance in the future.