Objective—To develop a reverse transcriptase-polymerase
chain reaction (RT-PCR) assay to detect
canine melanoma-associated antigens (MAAs) and to
use this technique to screen aspirates of lymph
nodes (LNs) for evidence of metastatic spread of oral
Animals—7 dogs with oral malignant melanoma and
4 dogs with multicentric lymphosarcoma.
Procedures—We prepared cDNA from melanoma
tumor biopsies and fine-needle aspirates obtained
from submandibular LNs of dogs with oral malignant
melanoma or multicentric lymphosarcoma. The RTPCR
assay was performed by use of tyrosinase,
Melan-A, gp100, tyrosinase-related protein 2 (TRP-2),
or melanoma antigen-encoding gene B (MAGE-B)-
Results—We detected MAGE-B mRNA in canine testicular
tissue but not in melanoma biopsy specimens.
Tyrosinase, Melan-A, gp100, and TRP-2 mRNAs were
detected in tumor biopsy specimens and in 2 of 5 LN
aspirates from dogs with melanoma, suggesting
metastatic spread in those 2 dogs. We did not detect
MAAs in LN aspirates obtained from dogs with multicentric
lymphosarcoma. Sequencing of canine Melan-
A and gp100 PCR products confirmed the specificity
of the assay for these genes.
Conclusions and Clinical Relevance—Clinical staging
of dogs with oral malignant melanoma is useful to
assist in designing appropriate treatments. However,
results of histologic examination of LN biopsy specimens
can be inconclusive and, in humans, can underestimate
the number of patients with metastatic disease.
Molecular staging of melanomas in dogs can be
achieved by screening LN aspirates for MAA mRNA,
and this can be performed in combination with cytologic
examination to aid in detection of metastatic disease.
( Am J Vet Res 2003;64:544–549)