Objectives To study angiogenesis in metastasis of unknown primary (MUP) to support the authors' hypothesis that MUPs are of a low angiogenic phenotype and are able to undergo metastasis in spite of an unknown primary.

Patients and methods A retrospective analysis was performed on paraffin blocks obtained from 50 cases of MUP and 52 cases of metastasis of known primary (MKP) from 1 January 2000 to December 2003. A prospective analysis was performed on fresh tissues from 22 cases of MUP and 26 cases of MKP. Immunohistochemical staining for VEGF was performed on the paraffin blocks. The fresh frozen tissue was analysed by RT-PCR and Western blotting for VEGF isoforms (VEGF₁₂₁, VEGF₁₆₅, VEGF₁₈₉) and VEGF protein, respectively.

Results Immunohistochemistry showed that MUPs had a higher percentage of lower scores of VEGF expression than MKPs. MKPs had increased scores of VEGF expression. RT-PCR analysis showed that MKPs had increased expression of VEGF₁₂₁ and VEGF₁₆₅ isoforms as compared with MUPs. MKPs showed a higher VEGF protein expression than MUPs.

Conclusion The study shows that metastases of squamous carcinoma from unknown primary have decreased VEGF expression at the immunohistochemical and protein level. They also display decreased expression of the VEGF₁₂₁ and VEGF₁₆₅ isoforms. Hence, these tumours are of a low angiogenic phenotype. They are able to develop a metastatic phenotype and grow at the metastatic site, since angiogenesis is redundant for lymph-node metastasis.