what are the classification of neoplasms ?
Classification of neoplasms.
Neoplasms are divided into benign and malignant. This is an important distinction, because it affects treatment and prognosis.
Benign neoplasms usually form a well circumscribed mass, while malignant neoplasms have poorly defined margins, with component cells infiltrating the surrounding tissues.
Benign neoplasms do not metastasis, while malignant ones do (they shed cells which grow at distant sites).
The cells of malignant neoplasms look more abnormal.
The differences are listed in more detail in the table below.
Feature Benign neoplasm Malignant neoplasm
Macroscopic appearance Discrete, smooth-surfaced Irregular or ill-defined outline
Microscopic margin Blunt, pushing Infiltrative, invasive
Nucleus:cytoplasm ratio Usually normal (1:4 or 1:6) Often high (1:1)
Nuclear pleomorphism Uncommon Common
Necrosis Very uncommon Often present
Mitotic rate Very low, normal mitoses Usually high, abnormal mitoses frequent
Clonality Oligo- or multiclonal Usually monoclonal
Metastases Never Often
Angiogenesis No Often
Differentiation Well differentiated Range from well differentiated to undifferentiated
Rate of Growth Slow growth over a period of yrs Rapid growth, sometimes erratic
Type of Growth Expansile (pushing margins) Progressive infiltration, invasion, and destruction of surrounding tissue
Separated from surrounding tissue? Yes
Has fibrous capsule composed of stroma of native tissue Poorly separated
Stromal invasion No Yes
Vascular invasion No Yes
Effect on host Often insignificant Significant
Cell shape Monomorphic Pleomorphic
Tumor giant cells
Nuclear chromatin Normal Increased, hyperchromatic
Peripheral clumping
Nucleoli Not prominent Prominent, w/ irregular shape
Neoplasms are also classified by the tissue of origin. There are six main groups:
1. Epithelial neoplasms, derived from epithelia, and from epithelial glandular structures.
2. Mesenchymal neoplasms, derived from tissues descended from mesenchyme: muscle, fibroblasts, bone, cartilage, fat, etc
3. Blood cell neoplasms, derived from cells descended from the pluripotent bone marrow stem cell.
4. Nervous system neoplasms, derived from cells of the central and peripheral nervous system.
5. Primative stem cell neoplasms.
6. Germ cell neoplasms
There are benign and malignant neoplasms in most of these groups. The nomenclature gives some information about the nature of the neoplasm:
The nomenclature
Neoplasms in general
All neoplasms have names ending in -oma. (Some other swellings do too, eg hamartoma, haematoma, granuloma).
Epithelial neoplasms
All benign epithelial neoplasms are adenomas (glandular morphology) or papillomas.
All malignant epithelial neoplasms end in -carcinoma. There are adenocarcinomas (glandular morphology), squamous cell carcinomas, transitional cell carcinomas (from epithelium of the urinary tract) and basal cell carcinomas.
Benign – end in –oma
Adenoma
An adenoma is a benign tumour of glandular or secretory epithelium
Tumors derived from glands, but not necessarily reproducing glandular patterns
Papillomas
A papilloma is a benign tumour of non-glandular or non-secretory epithelium
Produce microscopically or macroscopically visible finger-like or warty projections from epithelial surfaces
Malignant – ends in –carcinoma
Carcinoma is any malignant neoplasm of epithelial cell origin
Polypoid cancers = malignant polyps
Adenocarcinoma has a glandular growth pattern
Squamous cell carcinoma = malignant tumor of recognizable squamous cells in any epithelium of the body
Cell type/normal tissue Benign neoplasm Malignant neoplasm
Stratified squamous epithelium eg.skin Squamous cell papilloma Squamous cell carcinoma
Transitional cell epithelium eg. urogenital tract Transitional cell papilloma Transitional cell carcinoma
Glandular epithelium eg. gastrointestinal tract Adenoma Adenocarcinoma
Mesenchymal (connective tissue and muscle) neoplasms
All benign mesenchymal neoplasms start with an indication of the cell of origin, and end in -oma. All malignant mesenchymal neoplasms start with an indication of the cell of origin, and end in -sarcoma.
Benign tumors – end in –oma
Fibroma = benign tumor arising from fibroblastic cells
Meningioma = benign tumor of brain coverings
Leiomyoma = benign tumor of smooth muscle
Malignant tumors – end in –sarcoma
Have little connective tissue stroma and are fleshy
Fibrosarcoma
Sarcoma = any malignant neoplasm of mesenchymal origin
Normal Tissue Benign Neoplasm Malignant Neoplasm
Fibrous tissue (fibroblast) Fibroma Fibrosarcoma
Fat Lipoma Liposarcoma
Striated muscle Rhabdomyoma Rhabdomyosarcoma
Smooth muscle Leiomyoma Leiomyosarcoma
Cartilage Chondroma Chondrosarcoma
Bone Osteoma Osteosarcoma
Endothelium Haemangioma Angiosarcoma
Blood cell neoplasms
The distinction between benign and malignant is more difficult with neoplasms of blood cells as they usually do not form solid tissues. Some are more malignant than others, but it is difficult to say that any of them is benign. The nomenclature is confusing. There are four main groups of blood cell neoplasms: Leukaemias, Myeloproliferative disorders (essential thrombocythaemia, polycythaemia rubra vera, myelofibrosis, & CML), Lymphomas, & Myeloma. The -oma suffix of lymphoma and myeloma makes them seem benign, which they are not.
Nervous system neoplasms
Gliomas, neuromas. Meningiomas, ependymomas, and schwannomas, neurofibromas may be lumped in. Gliomas are malignant neoplasms derived from glial cells. The others are usually benign, but sometimes malignant. The nomenclature does not make any distinction.
Primitive stem cell neoplasms
All benign stem cell neoplasms start with an indication of the cell of origin, and end in -oma.
All malignant stem cell neoplasms start with an indication of the cell of origin, and end in -blastoma.
Normal tissue Benign neoplasm Malignant neoplasm
Kidney Cystic nephroma Nephroblastoma
Neural tissue Ganglioneuroma Neuroblastoma
Retina - Retinoblastoma
Germ cell neoplasms
Neoplasms derived from germ cells are called teratomas. They have the capacity to differentiate along more than one cell line and often contain both mesenchymal and epithelial elements. They may be benign or malignant depending on the degree of differentiation, and the nomenclature does not make any distinction.
Tetratoma – made up of a variety of parenchymal cell types representative of more than one germ layer, usually all three
Arise from totipotential cells that differentiate along various germ lines; can develop into any tissue of the body
Principally encountered in the gonads
Cystic tetratoma (dermoid cyst)
Ovarian
Differentiates along ectodermal lines to create a cystic tumor lined by skin replete w/ hair, sebaceous glands, and teeth str’s
Exceptions to Nomenclature:
• Following are malignant:
Mesothelioma
Melanoma Carcinomas of melanocytes
Seminoma Carcinomas of testicular origin
Heptatoma
Plasmacytoma
Lymphoma
Hypernephroma
Principal characteristics of carcinomas and sarcomas
Feature Carcinoma Sarcoma
Origin Epithelium Connective tissues
Behaviour Malignant Malignant
Frequency Common Relatively rare
Preferred route of metastasis Lymph Blood
In-situ phase Yes No
Age group Usually over 50 years Usually below 50 years
Choristoma – ectopic rest of normal tissue; example – rest of adrenal cells under the kidney capsule
Hamartoma
Aberrant differentiation produces a mass of disorganized, mature, specialized cells or tissue indigenous to the particular site
Example – Hamartoma in lung may contain islands of cartilage, blood vessels, bronchi, and lymphoid tissue
Totally benign
