The Histology of Rare Human Tumors and their Relationships to General Tumor Pathology

Abstract

Certain human tumors may be considered rare in the light of certain facts:

• the low percentage rate of certain cancers leads to a rare statistical level amongst tumors in general. This rarity is absolute for certain very rare cancers in all countries, and for all workers (such as the esthésioneurocytoma). It is relative for certain geographical distributions (hepatomas) and for age (example: adult nephroblastoma).

• the morphological rarity is represented by the fact that some relatively rare tumors sometimes show unusual histological aspects. These may be undifferentiated forms of usually differentiated cancers (anaplastic forms of osteogenic sarcomas), or unusual differentiations (rare epidermoid carcinomas of the stomach). This group is the main supply of Nadal Masson’s “ignotomas” which are the concern and sometimes the confusion of pathologists (Masson 1968).

• the rarity of their evolution is shown by the disconcerting behaviour of certain tumors with regard to their natural history. Either cancers which do not generally give rise to secondaries, develop visceral metastasis (such as the basal cell carcinoma of the skin). Or, an abnormally long evolution is found in patients with a very malignant tumor (melanomas, generalized carcinomas). Or, even spontaneous recovery is found (choriocarcinoma of the placenta, rare observations of glandular carcinomas).