Metastatic Tumors
Satish K. Tickoo, MD
Victor E. Reuter, MD
Key Facts
Terminology
Involvement of kidney by tumors originating in other organs
Direct extension from adjacent organs does not qualify as metastasis
Clinical Issues
Reported to constitute up to approximately 3% of all malignant renal tumors in surgical specimens
Kidney and ureter most common sites with metastatic tumors in urinary and male genital tract, followed closely by bladder
Often occurs as part of widespread tumor dissemination
In some cases, tumor may be solitary and mimic primary renal tumor
Most common reported sources of metastasis to kidney include lung (most common), colon-rectum, stomach, pancreas, uterus, and skin (melanoma)
Microscopic Pathology
Histologic features in metastatic carcinoma are commonly that of
Adenocarcinoma (30%), squamous cell carcinoma (28%), small cell carcinoma (8%), and malignant melanoma (6%)
Often show multinodular growth pattern, even when apparently well circumscribed on gross evaluation
Tumor emboli in vessels frequently present
Top Differential Diagnoses
Collecting duct carcinoma
Urothelial carcinoma
 This gross image shows a colonic adenocarcinoma metastatic to the kidney. Most metastatic tumors are multifocal and often bilateral. Solitary metastasis makes such a presumption clinically difficult. |
 This photomicrograph depicts a metastatic adenocarcinoma from a colorectal primary. In cases with atypical morphologic features for a renal primary, the clinical history is often crucial for proper diagnosis. |
TERMINOLOGY
Definitions
Involvement of kidney by tumors originating in other organs
Word “metastasis” is derived from Greek, meaning next placement or displacement
Almost always result of vascular or lymphatic spread from primary tumor
Direct extension from adjacent organs does not qualify as metastasis
Metastasis from contralateral kidney vs. bilateral primary tumors is extremely difficult to prove even when morphologically similar
Some hematopoietic malignancies involving kidney may also be considered metastatic but are not discussed here
CLINICAL ISSUES
Epidemiology
Incidence
Reported to constitute up to approximately 3% of all malignant renal tumors in surgical specimens
Kidney and ureter most common sites with metastatic tumors in urinary and male genital tract, followed closely by bladder
Metastases to kidney are reported to be higher in autopsy series, ranging from 9-20% in patients dying of tumors
Gender
Reported male to female ratio: 2.2:1 in older series
Higher incidence in males believed to be due to difference in lung cancer incidences over that time period
Presentation
Often occurs as part of widespread tumor dissemination
Renal involvement is frequently bilateral and multinodular in such situations
In some cases, tumor may be solitary and mimic primary renal tumor
Metastatic tumors to kidney presenting in surgical specimens these days are more likely to be mimickers of primary tumor
History of extrarenal primary in remote past may be obtained in most such cases on careful scrutiny
Very rarely, metastasis in kidney may be initial manifestation of primary tumor elsewhere
Most common reported sources of metastasis to kidney include
Lung (most common), colon-rectum, stomach, pancreas, uterus, and skin (malignant melanoma)
Other, much rarer sources include breast, salivary gland, and thyroid, among others
MACROSCOPIC FEATURES
General Features
Metastatic carcinomas are often multifocal and bilateral, particularly at autopsy
Concurrent metastatic involvement of other organ systems is very frequent in such a scenario
Occasionally, tumor may be unicentric, with no other clinically detectable metastatic tumors
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