Classification of neoplasms on histology basis

1. Histological assessment

Histology guides tumor behavior (benign / semi-malignant / malignant / borderline). Assessment establishes: tissue of origin (type), degree of differentiation/anaplasia, local invasion (vascular, lymphatic, perineural), metastasis, and other prognostic factors (e.g. estrogen receptors in breast cancer → better prognosis).

2. Classification by tissue of origin

Origin	Benign (-oma)	Malignant
Squamous epithelium	Squamous papilloma	Squamous cell carcinoma
Glandular/ductal epithelium	Adenoma, cystadenoma, papilloma	Adenocarcinoma, cystadenocarcinoma
Liver cells	Liver cell adenoma	Hepatocellular carcinoma
Connective tissue	Fibroma, lipoma, osteoma, chondroma	Fibrosarcoma, liposarcoma, osteosarcoma, chondrosarcoma
Muscle	Leiomyoma, rhabdomyoma	Leiomyosarcoma, rhabdomyosarcoma
Vessels	Hemangioma, lymphangioma	Angiosarcoma, lymphangiosarcoma
Blood/lymphoid	—	Leukemias, lymphomas
Salivary (mixed)	Pleomorphic adenoma	Malignant mixed tumor
Germ cells	Mature teratoma, dermoid cyst	Immature teratoma, teratocarcinoma

Naming exceptions (sound benign but are malignant): lymphoma, melanoma, mesothelioma, seminoma, hepatoma (HCC).

3. Differentiation

Extent to which tumor cells resemble the tissue of origin.

• Benign — well-differentiated, resemble normal counterpart (lipoma ≈ fat).
• Malignant — ranges from well-differentiated to undifferentiated; distinction from benign often relies on invasion/capsule breach.
• Endocrine benign tumors may overproduce hormones; poorly differentiated non-endocrine cancers may make ectopic hormones.

4. Anaplasia (hallmark of malignancy)

1. Pleomorphism — variation in cell/nuclear size & shape.
2. Block of maturation/dedifferentiation (e.g. AML).
3. Abnormal nuclei — ↑ N:C ratio, hyperchromasia, irregular shape, clumped chromatin.
4. Mitoses — numerous + atypical (tri-/multipolar).
5. Loss of polarity.
6. Progression via metaplasia → dysplasia → carcinoma in situ → invasion (e.g. bronchial squamous metaplasia).

💡 High-yield: Classify by tissue of origin + differentiation + invasion + metastasis. Epithelial malignant = carcinoma, mesenchymal = sarcoma. Watch exceptions: lymphoma/melanoma/mesothelioma/seminoma are malignant. Anaplasia (pleomorphism, ↑ N:C, atypical mitoses, loss of polarity) = hallmark of malignancy.