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• Neoplasia refers to new growth, where "Neo" means new and "Plasia" means creation (growth).
• Tumor means swelling.
• Neoplasia is defined as an abnormal mass of tissue.
• Neoplastic tissue grows more rapidly than normal tissue.
• Neoplastic growth is uncontrolled by normal growth control mechanisms and is autonomous.
• Neoplastic tissue competes with normal tissue for metabolic needs.
• Tumors are composed of cells and supporting stroma.
• Cells within a tumor are proliferating neoplastic cells.
• Tumors can be benign or malignant.
• Tumors start as monoclonal.
• Tumors are named according to their origin.
• Supporting stroma consists of non-neoplastic fibrous tissue and blood vessels derived from the host.

Classification of Tumors

• Tumors can be classified according to cell of origin and behavior.
• Tumors of epithelial or mesenchymal origin can be benign, malignant, or locally malignant.

Tumor Classification by Cell of Origin

• Benign tumors of epithelial origin include papillomas and adenomas.
• Papillomas originate from surface epithelium, examples include squamous cell papilloma and transitional cell papilloma.
• Adenomas originate from secretory epithelium, examples include tubular adenoma and liver cell adenoma.
• Malignant epithelial tumors are named with the tissue of origin + carcinoma, examples include squamous cell carcinoma, transitional cell carcinoma, and adeno-carcinoma.
• Benign mesenchymal tumors consist of the name of mesenchymal tissue + "oma," such as lipoma (from fat), chondroma (from cartilage), osteoma (from bone), leiomyoma (from smooth muscle), and rhabdomyoma (from skeletal muscle).
• Malignant mesenchymal tumors consist of name of mesenchymal tissue + "sarcoma," such as liposarcoma, chondrosarcoma, osteosarcoma, leiomyosarcoma, and rhabdomyosarcoma.
• Papilloma is a benign tumor of surface epithelium.
• Adenoma is a benign tumor of secretory epithelium.
• Carcinoma is a malignant tumor of epithelium.
• Rhabdomyoma is a benign tumor of skeletal muscles.
• Leiomyosarcoma is a malignant tumor of smooth muscles.
• Liposarcoma is a malignant tumor of fat cells.
• Neoplastic lesions ending in "oma" that are not neoplasms include hematoma, granuloma, and hamartoma.
• Malignant tumors ending in "oma" include melanoma, lymphoma, seminoma, glioma, and hepatoma.
• Leukemia is a malignant tumor of blood cells.

Tumor Classification According to Behavior

• Benign tumors are composed of normal cells.
• Malignant tumors are composed of normal or pre-malignant cells.
• Benign tumors grow slowly by expansion and push the surrounding normal tissue without tissue damage.
• Malignant tumors grow rapidly by both expansion and infiltration and infiltrate and damage the surrounding normal tissue.
• Benign tumors are single, small, and capsulated; they exhibit no hemorrhage or necrosis.
• Malignant tumors begin as single entities and then spread, reach a large size in a short time, are non-capsulated, and may exhibit hemorrhage or necrosis
• Benign tumors are inside solid organs or CT, capsulated mass.
• Malignant tumors are inside solid organs or CT, irregular non capsulated mass.
• Benign tumors arise from surface epithelia, forming non-capsulated polyps (papillomas).
• Malignant tumors arise from surface epithelia - taking different forms
• Malignant, Polypoid fungating mass.
• Malignant, Ulcerative pattern (malignant ulcer).
• Malignant, Infiltrative growth pattern (annular).
• Benign tumors have cells similar to the cell of origin and no criteria of malignancy.
• The pattern of arrangement of benign tumors is similar to the tissue of origin.
• Benign tumor stroma features few blood vessels, no hemorrhage, or necrosis.
• Benign tumors do not spread.
• Malignant tumors have cells showing criteria of malignancy
• The pattern of arrangement depends on tumor grade.
• The stroma of malignant tumors demonstrates prominent blood vessels, hemorrhage, and necrosis.
• Spread of malignant tumors occurs either directly into surrounding tissue or as distant metastasis via blood, lymphatic vessels, or through serous sacs (transcoelomic).
• Benign tumors have no recurrence.
• Malignant tumors recur (due to infiltrating borders with absence of capsule).
• Benign tumors are not harmful unless they occur in a vital organ, obstruct a hollow organ, produce hormones, or turn malignant.
• Malignant tumors are harmful due to organ destruction (infiltration), obstruction of hollow organs, and clinical syndromes related to the tumor.

Microscopic Criteria of Malignancy

• Pleomorphism (variability in cell and nuclear size and shape)
• Hyperchromatism (dense chromatin inside the nuclei)
• Increased N/C ratio to 1:2 (instead of 1:4 in normal cells)
• Tumor giant cells
• Atypical (abnormal) mitoses
• Prominent nucleoli

Tumor Grade

• The degree of similarity of tumor tissue to tissue of origin regarding morphology and function.
• Estimates the tumor aggressiveness.
• Grade I (well-differentiated tumors) have most tumor cells arranged similarly to the tissue of origin.
• Grade II (moderately differentiated tumors) have some tumor cells arranged similarly to the tissue of origin.
• Grade III (poorly differentiated tumors) have few tumor cells arranged similarly to the tissue of origin.
• Grade IV (undifferentiated/anaplastic tumors) exhibit no resemblance of tumor cells to tissue of origin.
• The term "anaplasia" indicates lost differentiation.
• Benign tumors are always well differentiated.
• Malignant tumors range from well-differentiated to completely undifferentiated.

Locally Malignant Tumors

• Tumors characterized by local infiltration, no blood or lymphatic spread, microscopic criteria of malignancy, recurrence after incomplete removal, and potential for malignant transformation.
• Examples, Adamantinoma of mandible, Basal cell carcinoma of the skin, Craniopharyngioma of pituitary gland, Carcinoid tumor, Giant cell tumor of bone.

Carcinoma and Sarcoma

• Carcinoma is a malignant tumor of surface epithelium, like squamous cell carcinoma or adenocarcinoma, and sarcoma is a malignant tumor of mesenchymal tissue, like liposarcoma or chondrosarcoma.
• Carcinomas are more common and occur in middle and old age, while sarcomas are less common and occur in young age
• Carcinomas grow slower, while sarcomas grow rapidly.
• Carcinomas spread via infiltration more than expansion and early via lymphatics, while sarcomas spread via expansion more than infiltration and early via blood.
• Carcinomas appear as irregular fixed masses in solid organs and fungating, ulcerating, or infiltrating masses in hollow organs, while sarcomas appear as coarsely nodular masses.
• Carcinomas have abundant stroma that separates sheets, groups, and acini with no stroma between individual cells, while sarcomas have scanty stroma that separates individual tumor cells.

Terminology of Neoplasia

• Tumor grade estimates tumor aggressiveness.
• Tumor stage is based on the TNM staging system, including the size of the primary tumor, presence or absence of lymph node spread, and presence or absence of metastasis (distant spread).