Liver Tumors Pathology — HCC and Metastases

Hepatocellular Carcinoma Molecular Pathogenesis

• Multi-step carcinogenesis in cirrhotic liver: Progressive transformation occurs through dysplastic nodules (small, <1 cm and large, >1 cm) that develop in regenerating cirrhotic liver tissue. Small dysplastic nodules show architectural and cytologic abnormalities with retained reticulin framework; large dysplastic nodules demonstrate increased malignant potential and may harbor foci of early HCC. TP53 mutations (>30% of HCC) occur early and confer loss of cell cycle checkpoints and apoptosis. CTNNB1 mutations activate Wnt/β-catenin signaling, promoting cell proliferation and survival. This transformation reflects cumulative genomic instability in hepatocytes exposed to chronic inflammatory cytokines (TNF-α, IL-6), oxidative stress, and viral oncoproteins.

• Chronic inflammation-driven carcinogenesis: HBV integration into hepatocyte DNA can disrupt tumor suppressors and activate oncogenes, while HCV core and NS5A proteins directly inhibit TP53 and promote cellular proliferation. Chronic alcohol exposure and NAFLD-related cirrhosis generate reactive oxygen species (ROS) that cause DNA damage and epigenetic alterations (DNA methylation, histone modifications). The cirrhotic microenvironment contains activated hepatic stellate cells producing TGF-β, which paradoxically promotes epithelial-mesenchymal transition (EMT) in transformed hepatocytes while simultaneously suppressing antitumor immunity.

• Hallmark molecular alterations: Three major molecular classes have been defined by TCGA: proliferation-related (MYC-driven, poor prognosis), differentiation-related (hepatocyte-differentiated, better prognosis), and intermediate/metabolic subtypes. FGF pathway activation (FGFR4 amplification) occurs in ~15% of HCC and represents a therapeutic target. MET amplification, TERT promoter mutations (>70% of HCC), and loss of chromosome 4q (containing TGF-β pathway genes) are frequent events. Immune checkpoint dysregulation includes PD-L1 upregulation and reduced T-cell infiltration.

Hepatitis B Virus (HBV) Infection

• Most common global risk factor; 80-90% of HCC in endemic regions occurs with HBV. Integration of HBV DNA into chromosome 17 can activate MYC or disrupt TP53. Chronic HBsAg positivity confers lifetime HCC risk of 15-25%. HBV X protein (HBx) directly transactivates viral and cellular genes, promoting transformation.

Hepatitis C Virus (HCV) Infection

• Accounts for 50-60% of HCC in developed Western countries. HCV requires cirrhosis as prerequisite (unlike HBV, which can cause HCC in non-cirrhotic livers). HCV core and NS5A proteins disable TP53 and interferon signaling. Genotype 1b and 3a carry higher carcinogenic risk.

Cirrhosis (Any Etiology)

• Underlying cirrhosis present in 80-90% of HCC cases globally. Advanced fibrosis (F3) already carries measurable HCC risk. Portal hypertension, shunting of portal blood away from hepatic detoxification, and angiogenesis in cirrhotic tissue promote tumor growth. The cirrhotic nodular architecture creates architectural alteration essential for dysplastic nodule formation.

Alcohol-Related Liver Disease

• Dose-dependent risk; >40-80 g/day for males, >20-40 g/day for females over >10 years. Ethanol metabolism generates acetaldehyde and ROS. Alcohol impairs hepatic antioxidant defenses and promotes lipid peroxidation. Synergistic HCC risk when combined with HBV or HCV.

Non-Alcoholic Fatty Liver Disease (NAFLD)

• Rapidly emerging HCC risk factor as obesity and metabolic syndrome prevalence increases. Can progress to non-alcoholic steatohepatitis (NASH) and cirrhosis. Lipotoxicity, mitochondrial dysfunction, and altered gut microbiota drive transformation. Paradoxically, HCC can develop in NAFLD without cirrhosis in ~10-30% of cases.

Hemochromatosis

• Iron overload promotes HCC through oxidative stress mechanisms and direct fibrogenic effects. Excess iron generates hydroxyl radicals via Fenton chemistry. Genetic hemochromatosis (HFE mutation) carries 5-10-fold increased HCC risk if cirrhosis develops.

Biliary Cirrhosis and Primary Biliary Cholangitis (PBC)

• Cholestasis-related toxins and bacterial lipopolysaccharide translocation promote fibrosis and HCC.

Aflatoxin B1 Exposure

• Dietary exposure in Africa and Asia; metabolized to aflatoxin B1-8,9-epoxide causing G→T transversions in TP53 (codon 249—characteristic "hotspot" mutation).

Anabolic Steroids and Estrogen

• Associated with benign hepatocellular adenoma, rarely HCC.

Genetic Syndromes

• Hereditary tyrosinemia, alpha-1 antitrypsin deficiency, Wilson disease, and Alagille syndrome carry elevated HCC risk.

Cardinal Symptoms and Signs in HCC

• Abdominal pain (40-50% of patients): Right upper quadrant or epigastric, reflecting tumor growth, necrosis, or hemorrhage within the mass. Morphologically corresponds to large infiltrative lesions causing hepatic distension.

• Hepatomegaly (40-80%): Firm, irregular, enlarged liver with palpable nodules representing tumor masses. In cirrhotic livers, hepatomegaly may be masked by cirrhotic contraction; absence does not exclude HCC.

• Jaundice (5-10%): Indicates advanced disease with hepatic decompensation or biliary obstruction by tumor. Reflects markedly reduced hepatic synthetic reserve and elevated bilirubin.

• Constitutional symptoms: Fever, weight loss, fatigue—present in 30-50% and indicate systemic inflammatory cytokine release (TNF-α, IL-6). Fever can also reflect tumor necrosis.

• Ascites (30-40%): Usually indicates underlying cirrhosis with portal hypertension rather than peritoneal carcinomatosis in early HCC. New or worsening ascites suggests HCC development in compensated cirrhosis.

• Variceal hemorrhage: May be presenting symptom when HCC develops in portal hypertensive patient.

• Paraneoplastic syndromes (15-20%): Erythrocytosis (EPO production), hypoglycemia (tumor glucose consumption), hypercalcemia (PTHrP production by poorly differentiated HCC), hypertrophic osteoarthropathy, diarrhea (VIP-secreting tumors—rare).

• Laboratory abnormalities:
• Elevated α-fetoprotein (AFP): Present in 50-70% of HCC; >400 ng/mL highly specific for HCC in cirrhotic patients. Normal in well-differentiated HCC (~20% of cases). AFP >20 ng/mL in cirrhotic patient warrants imaging surveillance.
• Elevated GGT and alkaline phosphatase: Suggests cholestasis from tumor or underlying liver disease.
• Thrombocytopenia: Reflects portal hypertension and bone marrow suppression.
• Anemia: May reflect hemolysis, bleeding, or chronic disease.
• Hypoglycemia: Ominous sign indicating large tumor burden or advanced disease.

• Imaging findings and morphological correlates:
• Arterial phase enhancement on CT/MRI: Reflects HCC's angiogenesis with recruitment of hepatic arterial blood supply. Well-differentiated tumors may not enhance; poorly differentiated tumors show brisk enhancement.
• Washout in portal venous or delayed phase: Characteristic HCC pattern; benign lesions typically retain contrast.

Histological Features of Hepatocellular Carcinoma

• Well-differentiated HCC: Tumor cells arranged in plates or trabecular pattern mimicking normal hepatocyte cords, 1-2 cells thick. Increased nuclear-to-cytoplasmic (N:C) ratio, hyperchromatic nuclei, and mild pleomorphism. Reticulin stain shows loss or distortion of normal hepatocyte-sinusoid relationship (compared to retained framework in dysplastic nodules). Increased mitotic rate. Minimal cytologic atypia may necessitate immunohistochemistry (IHC) for confirmation.

• Intermediate-differentiated HCC: Thicker trabecular plates (>2 cells), increased atypia, prominent nucleoli, and more frequent mitoses. Glandular/acinar differentiation with some mucin production. Clear distinction from dysplastic nodules becomes more apparent.

• Poorly differentiated HCC: Solid sheet-like architecture with marked cytologic pleomorphism, high N:C ratio, atypical mitotic figures, and massive necrosis. May mimic other malignancies; IHC essential. Loss of hepatocyte marker expression (hepatocyte paraffin 1, arginase-1). High Ki-67 proliferation index.

• Special histological subtypes:
• Fibrolamellar HCC: Rare variant in non-cirrhotic livers; prominent fibrous septa separate nests of tumor cells. Better prognosis than conventional HCC. Characterized by DNAJB1-PRKACA fusion gene (90% of cases). Typically presents in young patients (median age 20-30 years).
• HCC with sarcomatoid differentiation: Spindle cell component indicating poor differentiation and aggressive behavior.
• HCC with cholangiocellular differentiation: Mixed hepatocellular-cholangiocarcinoma; intermediate prognosis.
• Clear cell HCC: Tumor cells rich in glycogen or lipid; must exclude metastatic renal cell carcinoma or adrenocortical carcinoma.

• Immunohistochemical Panel (critical for diagnosis):
• Hepatocyte markers (positive in HCC): Hepatocyte paraffin 1 (HepPar1), arginase-1, glypican-3, alpha-fetoprotein
• Markers of increased proliferation/poor differentiation: Ki-67 (>10% in well-differentiated, >30% in poorly differentiated), CK19 (indicates poor prognosis and potential stem cell features)
• Cytokeratin 7/19 positivity: Associated with worse prognosis, particularly in small tumors
• Negative markers: CK20 (positive in colorectal metastases), CDX2, TTF-1 (lung origin), PSA (prostate origin)

• Gross Pathology Appearance:
• Color and consistency: Tan to gray-white, soft, compressible mass (compared to firm cirrhotic liver background). Advanced tumors may show areas of hemorrhage, necrosis, and cystic degeneration.
• Margins: Well-circumscribed lesions in non-cirrhotic liver; infiltrative margins in cirrhosis with satellite nodules reflecting portal vein invasion.
• Encapsulation: Pseudocapsule of compressed hepatic tissue and fibrosis may be present; true fibrous capsule rare. Capsular invasion indicates higher grade.
• Size at diagnosis: Varies widely; Western patients typically present with larger tumors (median 5-7 cm) due to late detection. Asian patients with surveillance programs present with smaller tumors.

• Diagnostic Criteria (AASLD/EASL Guidelines):
• Lesions >1 cm in nodule, <1 cm in context of cirrhosis in cirrhotic patient: Diagnosis by single imaging modality showing arterial phase enhancement + washout, OR pathological proof.
• Lesions 1-2 cm: Require two concordant imaging modalities (CT, MRI, ultrasound) showing characteristic pattern OR one imaging modality plus AFP >400 ng/mL OR pathological proof.
• Lesions >2 cm: Single imaging modality showing arterial enhancement and washout sufficient for diagnosis.
• Nodules <1 cm in cirrhotic liver: Surveillance (ultrasound every 3 months) unless AFP dramatically elevated.

• Laboratory and Tumor Markers:
• AFP (α-fetoprotein): Baseline prognostic value; kinetic increase (doubling time <20 days) suggests rapid growth.
• PIVKA-II (prothrombin induced by vitamin K absence): Des-gamma-carboxyprothrombin; positive in AFP-negative HCC; associated with vascular invasion.
• MicroRNA signatures: miR-122, miR-224 underexpressed in HCC; emerging research biomarkers.

• Molecular/Genetic Testing (prognostic, increasingly therapeutic):
• TP53 mutations: Associated with poor prognosis, high grade.
• CTNNB1 mutations: Associated with better prognosis in some cohorts but linked to advanced features.
• TERT promoter mutations: Prognostic significance debated.
• Genomic subclasses: TCGA classification (Proliferation-High, Hepatocyte-Differentiated, Intermediate, Mixed) predicts outcomes and response to systemic therapy.

Surgical Resection (First-Line for Resectable Tumors)

• Indications: Single tumors <5 cm or 2-3 tumors <3 cm in cirrhotic livers with preserved hepatic function (Child-Pugh A, adequate portal vein patency, normal bilirubin, platelet >100k). Hepatic resection in cirrhotic patients requires careful assessment of hepatic reserve (hepatic venous pressure gradient, indocyanine green retention, volume analysis by CT).
• Rationale: Curative intent in selected patients with 5-year survival rates of 40-70% for early-stage disease when negative margins (R0) achieved. Requires 2-3 cm normal liver margin in non-cirrhotic livers; 1 cm margin sufficient in cirrhosis given chemoprevention effect of resection on remaining cirrhotic tissue.
• Perioperative complications: Hepatic insufficiency (occurs in <5% with proper selection), bleeding, bile leak, infection. Portal vein thrombosis can develop postoperatively; risk stratified by preoperative PVT presence.

Liver Transplantation (First-Line for Early HCC + Cirrhosis/Decompensation)

• Indications (Milan Criteria): Single tumor ≤5 cm OR 2-3 tumors each ≤3 cm with no extrahepatic metastases or macrovascular invasion. Expanded criteria (UCSF: single ≤6.5 cm or 2-3 tumors, largest ≤4.5 cm, total tumor diameter ≤8 cm) show acceptable outcomes in selected centers.
• Rationale: Optimal treatment when HCC develops in decompensated cirrhosis; removes both tumor and cirrhotic liver, eliminating risk of recurrent HCC and treating portal hypertension. Excellent long-term outcomes (5-year survival 60-70%) within Milan Criteria; intention-to-treat outcomes lower (40-50%) due to dropout from waitlist.
• Neoadjuvant therapy while awaiting transplant: Bridging therapies (transarterial chemoembolization [TACE], sorafenib) used to prevent progression beyond transplant criteria.

Tumor-related complications

• Spontaneous tumor rupture with hemoperitoneum (emergency): an exophytic, subcapsular HCC outgrows its arterial supply, necroses, and bleeds into the peritoneum. Signals: abrupt RUQ pain with hypotension, falling hematocrit, and hemoperitoneum with sentinel clot adjacent to the tumor on CT. Resuscitation plus transarterial embolization is the usual first maneuver, with resection deferred, per NCCN Hepatobiliary Cancers guidance.
• Portal vein tumor thrombus: HCC's propensity for vascular invasion. Signal: an expansile thrombus that enhances in the arterial phase (a bland thrombus does not). This upstages disease to advanced (BCLC C), excludes Milan criteria, and may precipitate new ascites or variceal bleeding.
• Hepatic vein/IVC invasion: produces *Budd-Chiari*-like outflow obstruction and, rarely, tumor pulmonary embolism.
• Hepatic decompensation: tumor replacement plus underlying cirrhosis yields jaundice, encephalopathy, refractory ascites. Variceal hemorrhage is an emergency — vasoactive therapy (octreotide), prophylactic ceftriaxone, and urgent endoscopy per AASLD portal hypertension guidance.
• Paraneoplastic syndromes: hypoglycemia from big-IGF-2, erythrocytosis from EPO, hypercalcemia from PTHrP. Symptomatic hypoglycemia and hypercalcemic crisis require emergent treatment.
• Metastatic sequelae: lung is the most common extrahepatic site; lytic bone lesions can cause cord compression (emergency). For hepatic metastases generally, hilar nodal or intrahepatic biliary compression causes obstructive jaundice, and hepatic replacement by neuroendocrine metastases permits carcinoid syndrome by bypassing first-pass serotonin clearance.

Treatment-related complications

• Post-hepatectomy liver failure: inadequate future liver remnant in a cirrhotic; signaled by rising bilirubin and INR persisting past postoperative day 5.
• Post-embolization syndrome after TACE: ischemic tumor necrosis causing fever, pain, and transaminitis; self-limited. Distinguish from nontarget embolization causing liver abscess, ischemic cholecystitis, or acute-on-chronic liver failure.
• Post-transplant hepatic artery thrombosis (emergency): biliary tree depends solely on arterial flow, so thrombosis causes ischemic biliary necrosis and graft loss; suspect with abrupt transaminase rise and confirm with Doppler.
• Systemic therapy: bevacizumab (with atezolizumab) raises variceal bleeding and GI perforation risk — screening endoscopy before initiation is standard; checkpoint inhibitors cause immune hepatitis and colitis; multikinase inhibitors (sorafenib, lenvatinib) cause hand-foot skin reaction and hypertension.

• Surveillance is the tested behavior: AASLD recommends abdominal ultrasound with or without AFP at 6-month intervals in patients with cirrhosis and in selected chronic HBV carriers. A stem describing a cirrhotic patient who has never had surveillance is asking for ultrasound, not CT.
• Single best next step for a new nodule in a cirrhotic liver: multiphasic contrast-enhanced CT or MRI — not biopsy. HCC is the classic solid tumor diagnosed radiographically: arterial phase hyperenhancement plus portal-venous/delayed washout (ACR LI-RADS criteria) is sufficient. Biopsy is reserved for indeterminate lesions and carries a small tract-seeding and bleeding risk.
• Aflatoxin B1 → TP53 codon 249 G→T transversion is the single most reliably tested environmental–molecular association; look for stored grains/peanuts in sub-Saharan Africa or East Asia, often with coexisting HBV.
• Fibrolamellar HCC: adolescent or young adult, non-cirrhotic liver, normal AFP, lamellar fibrous bands separating polygonal eosinophilic cells, DNAJB1-PRKACA fusion. The distractor is assuming cirrhosis and a high AFP — their absence does not exclude malignancy.
• HBV can cause HCC without cirrhosis (viral DNA integration is directly mutagenic); HCV essentially requires cirrhosis first. NAFLD/NASH is the other rising cause of non-cirrhotic HCC.
• In the US, metastases outnumber primary liver cancer. Multiple nodules of varying size scattered through a non-cirrhotic liver, often with umbilicated capsular deposits, means metastasis — colon, lung, breast, pancreas. Immunohistochemistry settles it: CK20/CDX2 positive = colorectal; TTF-1 = lung; HepPar1, arginase-1, glypican-3 = hepatocellular.
• Vascular invasion is the HCC signature: portal vein tumor thrombus that enhances arterially. The distractor is calling it bland portal vein thrombosis from cirrhosis alone.
• Do not confuse benign mimics: cavernous hemangioma (most common benign liver tumor, peripheral nodular discontinuous enhancement with centripetal fill-in), focal nodular hyperplasia (central stellate scar, female, benign), and hepatic adenoma (oral contraceptives or anabolic steroids, risk of rupture and bleeding, β-catenin-activated subtype risks malignant transformation).