Definition/General
Introduction:
Pulmonary metastases are secondary malignancies in the lung
More common than primary lung cancer
Lungs are common metastatic site
Result from hematogenous or lymphatic spread
Multiple primary sites.
Origin:
Secondary spread from extrapulmonary primary malignancies
Hematogenous dissemination most common
Lymphatic spread
Direct extension
Pleural seeding.
Classification:
Based on primary site: Breast, colorectal, kidney, sarcoma, melanoma, etc
Pattern: Nodular, lymphangitic, miliary
Number: Solitary vs multiple
Timing: Synchronous vs metachronous.
Epidemiology:
Common occurrence
30% of cancer patients develop lung metastases
Breast, colorectal, kidney most common primaries
Any age depending on primary
Variable prognosis.
Clinical Features
Presentation:
Often asymptomatic
Dyspnea
Cough
Chest pain
Hemoptysis
Constitutional symptoms
Pleural effusion.
Symptoms:
Shortness of breath
Persistent cough
Chest discomfort
Weight loss
Fatigue
Bone pain (rib metastases)
Superior vena cava syndrome.
Risk Factors:
Known primary malignancy
Advanced stage primary
Vascular invasion
Lymph node involvement
High-grade histology
Certain histologic types.
Screening:
CT chest
Multiple pulmonary nodules
Staging workup
PET-CT scan
Comparison with primary
Tissue confirmation.
Master Lung Metastases Pathology with RxDx
Access 100+ pathology videos and expert guidance with the RxDx app
Gross Description
Appearance:
Multiple nodules
Well-circumscribed
Variable sizes
Gray-white, firm
Peripheral distribution
Bilateral involvement.
Characteristics:
Round, discrete nodules
Firm consistency
Homogeneous cut surface
Resembles primary tumor
Pleural-based lesions
Hemorrhage/necrosis variable.
Size Location:
Peripheral subpleural
Multiple bilateral nodules
Variable sizes (0.5-10 cm)
Lower lobe predilection
Pleural involvement
Hilar lymphadenopathy.
Multifocality:
Multiple lesions typical
Bilateral distribution
Different sizes
Cannon-ball lesions (large, round)
Miliary pattern
Lymphangitic spread.
Microscopic Description
Histological Features:
Histology reflects primary site
Adenocarcinoma (breast, lung, GI)
Squamous carcinoma (head/neck, cervix)
Sarcoma (bone, soft tissue)
Melanoma
Neuroendocrine tumors.
Cellular Characteristics:
Morphology matches primary
Well to poorly differentiated
Glandular formation (adenocarcinoma)
Spindle cells (sarcoma)
Melanin pigment (melanoma)
Neuroendocrine features.
Architectural Patterns:
Nodular replacement
Lymphangitic pattern
Perivascular distribution
Pleural involvement
Interstitial infiltration
Cavitation (squamous).
Grading Criteria:
Based on primary tumor
Grade maintained in metastases
Differentiation assessment
Mitotic activity
Necrosis evaluation.
Immunohistochemistry
Positive Markers:
Site-specific markers: TTF1 (lung), PSA (prostate), ER/PR (breast), CDX2 (GI), PAX8 (kidney, thyroid), S-100 (melanoma)
Cytokeratins
Vimentin (sarcoma).
Negative Markers:
Variable based on primary
Lung-specific markers often negative
Multiple primaries exclusion.
Diagnostic Utility:
Primary site identification
Organ-specific markers crucial
CK7/CK20 pattern
TTF1 distinguishes lung primary
Panel approach essential.
Molecular Subtypes:
Breast metastases: ER+, PR+, HER2+/-
Colorectal: CDX2+, CK20+
Renal: PAX8+, CD10+
Prostate: PSA+, NKX3.1+
Melanoma: S-100+, Melan-A+.
Molecular/Genetic
Genetic Mutations:
Retain primary tumor genetics
Additional mutations possible
EGFR mutations (lung adenocarcinoma)
KRAS mutations (colorectal)
BRAF mutations (melanoma).
Molecular Markers:
Maintain primary characteristics
Hormone receptors (breast)
Microsatellite status (colorectal)
PD-L1 expression
Mutation burden.
Prognostic Significance:
Primary site most important
Number of metastases
Size of lesions
Performance status
Disease-free interval
Response to treatment.
Therapeutic Targets:
Primary tumor therapy
Surgical resection (oligometastases)
Chemotherapy
Targeted therapy
Immunotherapy
Radiation therapy.
Differential Diagnosis
Similar Entities:
Primary lung carcinoma
Multiple primary tumors
Lymphoma
Infectious diseases
Inflammatory conditions.
Distinguishing Features:
Metastases: Multiple nodules, primary site markers+
Primary lung: TTF1+, single lesion
Multiple primaries: Different morphology
Lymphoma: CD45+
Infection: Inflammatory infiltrate.
Diagnostic Challenges:
Unknown primary
Poorly differentiated carcinoma
Multiple primaries
Synchronous vs metachronous
Small biopsies.
Rare Variants:
Choriocarcinoma metastases
Germ cell tumor metastases
Neuroendocrine metastases
Leiomyosarcoma metastases.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[Wedge resection/biopsy] with multiple pulmonary nodules
Nodule Description
[Number] well-circumscribed nodules ranging from [X] to [X] cm
Microscopic Features
Metastatic [carcinoma/sarcoma/melanoma] with morphology consistent with [primary site] origin
Primary Site Correlation
Morphologic features consistent with known [primary site] carcinoma
Immunohistochemistry
[Site-specific markers]: [Results], CK7: [Result], CK20: [Result], TTF1: [Negative/Positive]
Grade
[Well/moderately/poorly] differentiated, similar to primary tumor
Molecular Correlation
[Molecular features consistent with primary tumor if available]
Staging
M1 disease - distant metastases present
Final Diagnosis
Metastatic [tumor type] to lung, consistent with [primary site] origin
Clinical Correlation
Findings consistent with pulmonary metastases from known [primary site] malignancy