Definition/General

Introduction:
-Metastatic tumors to the kidney represent secondary malignancies from distant primary sites
-They constitute 2-3% of all renal masses on imaging
-However, autopsy studies show much higher incidence (up to 20%)
-FNAC plays crucial role in diagnosis and staging.
Origin:
-Arise from hematogenous spread from primary tumors
-Lymphatic spread also possible
-Direct extension from adjacent organs
-Common primary sites include lung, breast, gastrointestinal tract
-Kidney has rich vascular supply facilitating metastatic spread.
Classification:
-Classified by primary site of origin
-Carcinomas most common (adenocarcinoma, squamous cell carcinoma)
-Hematologic malignancies (lymphoma, leukemia)
-Sarcomas (rare)
-Melanoma
-Neuroendocrine tumors.
Epidemiology:
-More common in elderly patients
-Often discovered during staging workup of known primary tumors
-Bilateral involvement more common than in primary renal tumors
-Multiple lesions characteristic
-Indian population shows similar patterns with regional cancer variations.

Clinical Features

Presentation:
-Often asymptomatic (incidental finding on staging studies)
-Known primary tumor in majority of cases
-Flank pain (if large)
-Hematuria (uncommon)
-Multiple renal lesions on imaging
-Bilateral involvement possible.
Symptoms:
-Usually symptoms related to primary tumor predominate
-Constitutional symptoms (weight loss, fatigue)
-Flank pain (mass effect)
-Renal dysfunction (if extensive involvement)
-Hematuria rare
-Paraneoplastic syndromes from primary tumor.
Risk Factors:
-History of malignancy (most important)
-Advanced stage primary tumor
-Immunocompromised state
-Previous chemotherapy or radiation
-Certain primary sites (lung, breast, melanoma)
-Multiple primary tumors.

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Gross Description

Appearance:
-Multiple small nodules scattered throughout both kidneys
-Well-demarcated lesions
-Variable color depending on primary tumor type
-Size typically small to medium (0.5-5 cm)
-Preservation of renal architecture.
Characteristics:
-Gray-white nodules most common
-Tan to brown (depending on primary)
-Hemorrhagic areas possible (melanoma, RCC)
-Mucoid appearance (mucinous adenocarcinomas)
-No central necrosis typically.

Microscopic Description

Immunohistochemistry

Molecular/Genetic

Differential Diagnosis

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.

Clinical History

Patient with known [primary tumor type] diagnosed in [date]. Current imaging shows [renal lesion characteristics]

Specimen Information

FNAC from [renal lesion/kidney mass], performed under [guidance method]

Specimen Adequacy

[Adequate/Inadequate] for cytological interpretation

Cytological Findings

Cellular smears showing [morphological pattern consistent with primary tumor type]. Features include [specific characteristics]

Comparison with Primary

Morphological features [consistent/similar] to known [primary tumor type]

Immunocytochemistry

[Marker panel] performed: [Results consistent with primary site]

Cytological Diagnosis

[Metastatic carcinoma] - Consistent with metastasis from [primary site]

Staging Implications

Findings consistent with [M1 disease/distant metastasis]. Multidisciplinary team discussion recommended

Recommendations

[Additional molecular studies/Comparison with primary tumor/Clinical correlation] as indicated

Note

Treatment planning should involve multidisciplinary team including medical oncology