Histology and Classification of Tumors

Neoplasia (tumors) are abnormal tissue proliferations, which develop exceeding normal tissue, uncoordinated with it. This uncontrolled tissue growing may continue even after cessation of the etiologic factor (self-maintained). The structure of a tumor (neoplasia) : parenchyma (tumor cells derived from previously normal cells) and stroma (vessels and connective tissue), in variable proportions.

Classification and nomenclature of tumors

Tumours composed of one parenchymal cell type	Benign	Malignant
1. Epithelial tumours
Stratified squamous epithelium	Squamous cell papilloma	Squamous cell carcinoma
Basal cells of skin or adnexa	Seborrheic keratosis	Basal cell carcinoma
Glands or ducts	Adenoma (adenomatous polyp) Cystadenoma	Adenocarcinoma Papillary carcinoma Cystadenocarcinoma
Respiratory tract epithelium		Bronchogenic carcinoma
Neuroectoderm	Melanocytic nevus	Malignant melanoma
Renal epithelium	Renal tubular adenoma	Renal cell carcinoma
Liver cells	Liver cell adenoma	Hepatocellular carcinoma
Bile ducts	Billiary adenoma	Bile duct carcinoma
Urinary tract epithelium (transitional)	Transitional cell papilloma	Transitional cell carcinoma
Placental epithelium - gestational trophoblast	Hydatidiform mole	Gestational choriocarcinoma
2. Mesenchymal tumours
Conjunctive tissue and derivatives : fibroblasts lipoblasts chondroblasts osteoblast	Fibroma Lipoma Chondroma Osteoma	Fibrosarcoma Liposarcoma Chondrosarcoma Osteogenic sarcoma
Endothelium and relative tissues : blood vessels lymphatic vessels synovia mesotelium meninge	Hemangioma Lymphangioma Solitary fibrous tumour of the pleura Meningioma	Angiosarcoma Lymphangiosarcoma Synoviosarcoma Malignant mesothelioma Invazive meningioma
Blood cells : hematopoietic cells lymphoid tissue		Leukemias Malignant lymphomas (Hodgkin's and non-Hodgkin's lymphomas)
Muscle fibers : smooth striated	Leiomyoma Rhabdomyoma	Leiomyosarcoma Rhabdomyosarcoma

Tumours with different types of cells from the same germ layer - mixed tumours	Benign	Malignant
Salivary glands	Pleomorphic adenoma (Mixed tumour of salivary gland origin)	Malignant mixt tumour of salivary gland origin
Breast	Fibroadenoma	Malignant cystosarcoma phyllodes
Nephroblastem (metanephric blastema)		Nephroblastoma (Wilms' tumor)

Tumours with different types of cells derived from more than one germ layer - teratogenous	Benign	Malignant
Totipotential cells in gonads or in embryonic rests	Mature teratoma Dermoid cyst	Immature teratoma Teratocarcinoma (Embryonic carcinoma) Endodermal sinus tumour Non-gestational choriocarcinoma