What is Adenocarcinoma
Adenocarcinoma is a malignant epithelial tumor characterized by glandular or acinar differentiation, papillary structures, and cytoplasmic mucin vacuoles. 1
Core Pathologic Definition
Adenocarcinoma represents a broad category of cancers arising from glandular epithelial cells that can occur in virtually any organ system. The defining microscopic features include:
- Glandular or acinar differentiation visible at the light microscopic level, forming recognizable gland-like structures 1
- Papillary architectural patterns with finger-like projections of tumor cells 1
- Cytoplasmic mucin vacuoles within malignant cells 1
- Invasion through the basement membrane, distinguishing it from in situ disease 1
The diagnosis can be supported by special stains for mucin or immunohistochemical markers of ductal differentiation such as cytokeratin 19. 1
Histologic Subtypes and Grading
Adenocarcinomas are classified into multiple histologic subtypes depending on their architectural patterns:
Common Subtypes
- Acinar adenocarcinoma: Forms well-defined glandular structures 1
- Papillary adenocarcinoma: Characterized by papillary projections 1
- Micropapillary adenocarcinoma: Small rounded tumor cell clusters within stromal spaces, associated with adverse features including lymphovascular invasion 1
- Solid adenocarcinoma: Lacks glandular architecture, considered high-grade 1
- Mucinous adenocarcinoma: Contains >50% extracellular mucin pools with malignant glands or individual tumor cells 1
- Signet-ring cell adenocarcinoma: >50% of tumor shows signet-ring morphology with intracytoplasmic mucin displacing nuclei, associated with worse stage-for-stage survival 1
Grading System
Adenocarcinomas are graded based on architectural and cytologic features: 1
- Well-differentiated (Grade 1): Well-defined glands with minimal nuclear pleomorphism, few mitoses 1
- Moderately differentiated (Grade 2): Disorganized growth with less defined glands, increased nuclear pleomorphism and mitoses 1
- Poorly differentiated (Grade 3): Small poorly defined glands, individual infiltrating cells, solid areas, prominent nuclear pleomorphism, frequent mitoses 1
Histologic grading provides prognostic information regarding likelihood of nodal metastases and overall survival. 1
Organ-Specific Characteristics
Lung Adenocarcinoma
The most common form of lung cancer, characterized by peripheral location and often associated with a desmoplastic stromal response. 1 Subtypes include acinar, papillary, micropapillary, and solid patterns, frequently presenting as composite subtypes. 1
Colorectal Adenocarcinoma
Almost all colorectal cancers are adenocarcinomas, most classified as "not otherwise specified" (NOS). 1 Specific subtypes carry distinct prognostic implications, with signet-ring cell variant showing worse survival and medullary carcinoma demonstrating better prognosis. 1
Pancreatic Adenocarcinoma
Invasive ductal adenocarcinoma represents the vast majority of pancreatic malignancies, characterized by ductal differentiation and intense desmoplastic reaction. 1 Subtypes include tubular, adenosquamous, colloid (mucinous noncystic), and medullary variants. 1
Cervical Adenocarcinoma
Accounts for 10-25% of cervical cancers with rising incidence, often HPV-associated (particularly HPV-18), presenting diagnostic challenges due to endocervical location. 2, 3, 4 Shows greater propensity for lymph node and distant metastases compared to squamous cell carcinoma. 2, 3
Clinical Significance
Desmoplasia (cellular fibroinflammatory response) characteristically accompanies invasive adenocarcinomas, representing the host stromal response rather than pre-existing scar tissue. 1 This feature is particularly prominent in pancreatic, breast, and lung adenocarcinomas. 1
The heterogeneity of adenocarcinomas—both between different organ sites and within individual tumors—represents a major clinical challenge affecting treatment response and prognosis. 5 Accurate histologic subtyping and grading are essential for appropriate treatment planning and prognostic stratification. 1