When diagnosing a malignant tumor it is important to determine whether the tumor is a primary or metastatic one. While useful all of these heuristics have their exceptions.
Finding
Favor Primary
Favor Metastasis
precursor lesion (dysplasia, etc) at site
present, or history of
absent
size and location
small and mucosal (low stage)
large and outer wall
growth direction
outwards
inwards
evidence elsewhere of a tumor, or history of
none
present, especially if from past history and same histologic type
number of tumors
single
multiple
frequency of tumor type at site
common
rare
marker studies
consistent with site
inconsistent with site
where:
• A large tumor may replace any precursor lesion. A patient with poor or no records may not have evidence of a precursor lesion.
• The presence of tumor elsewhere could represent a metastasis from the location.
• A person with synchronous tumors can have multiple primary lesions.
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