What is carcinoma?

What is Carcinoma?

Carcinoma is a malignant neoplasm arising from epithelial cells that line organs and tissues throughout the body. 1, 2

Fundamental Definition and Origin

Carcinoma represents cancer that originates specifically from epithelial tissue, distinguishing it from other cancer types like sarcomas (which arise from connective tissue) or lymphomas (which arise from lymphoid cells). 2 The defining characteristic is that these malignant cells derive from the epithelial cells that form the lining of organs, ducts, and body surfaces. 3

Prevalence and Clinical Significance

• Carcinomas account for 80-100% of all human cancers, making them by far the most common type of malignancy. 3, 4
• The most common carcinomas include prostate cancer in males, breast cancer in females, and lung carcinoma (the leading cause of cancer-related mortality in the United States). 2
• Adenocarcinomas—a subtype arising from glandular epithelial cells lining ducts—represent the most common form of carcinoma. 4

Pathologic Characteristics

The diagnosis of carcinoma is made based on both cytologic features (cellular appearance) and architectural patterns, along with the location of proliferating cells and their interaction with surrounding stromal elements. 2

Key Diagnostic Features:

• Invasion through the basement membrane is the critical transition from pre-invasive to invasive carcinoma. 2, 3
• Once cells breach the basement membrane, they gain potential to invade blood vessels or lymphatic channels, leading to metastasis and significantly increased morbidity and mortality. 2
• Carcinomas typically begin as clonal proliferations of cells with acquired mutations that progress to invasive disease. 2

Histologic Subtypes

Different carcinoma subtypes are recognized based on their differentiation patterns:

Squamous Cell Carcinoma

• Composed of cells with recognizable squamous differentiation 1
• Can be keratinizing (with keratin pearls) or nonkeratinizing 1
• Account for approximately 70-80% of cervical cancers 1

Adenocarcinoma

• Shows glandular or ductal differentiation 1
• Includes tubular, mucinous, colloid, and papillary variants 1
• Account for 10-15% of cervical cancers but are more common in other organs 1

Adenosquamous Carcinoma

• Contains significant components of both ductal and squamous differentiation 1

Undifferentiated Carcinoma

• Shows no glandular, acinar, endocrine, or squamous differentiation 1
• Can have anaplastic giant cell or sarcomatoid morphology 1

Medullary Carcinoma

• Characterized by poor differentiation, syncytial growth pattern, pushing borders, and necrosis 1

Important Clinical Distinctions

Carcinosarcomas (also called malignant mixed Müllerian tumors) are now understood to be metaplastic carcinomas, not sarcomas, despite their name and biphasic appearance. 1 This reclassification is critical because it affects staging and treatment approaches—they are staged as high-grade endometrial cancers rather than sarcomas. 1

Metaplastic breast carcinomas (carcinosarcomas of the breast) are epithelial neoplasms and should be treated according to their primarily epithelial nature, not as sarcomas. 1

Epithelial-to-Mesenchymal Transition (EMT)

The breakdown of epithelial cell homeostasis leading to aggressive cancer progression correlates with loss of epithelial characteristics and acquisition of a migratory phenotype—a phenomenon called epithelial-to-mesenchymal transition (EMT). 5 This is considered a crucial event in late-stage tumorigenesis and local invasion. 5

Clinical Implications

• Early detection is critical because carcinomas at epithelial surfaces are often accessible to inspection and intervention before invasion or metastasis occurs. 3
• Good prognosis with long-term disease-free survival is more likely when detection occurs before significant invasion or intravasation into blood vessels. 3
• The molecular characteristics of carcinomas increasingly guide treatment decisions, with targeted therapies developed based on specific genetic alterations. 6