Q2: Choosing Primary vs. Metastatic Tissue for Canine CGP Analysis

We’ve received many questions about whether to analyze primary or metastatic tissue. While each case is unique, here are some general guidelines:

1. If the lymph node or other mets tissue is sampled at the same time as the primary tumor, we’ll use whichever sample has the best quality. For example, if the primary tumor shows extensive necrosis or low tumor cellularity, we would use the lymph node or other mets tissue. If quality is similar, we typically prioritize the primary tumor, as it most directly reflects the tumor’s biology at diagnosis and is more representative of different tumor clones.
2. If the metastatic site is collected much later (e.g. after 6-9 months under treatment), then the mets may provide more up-to-date and clinically relevant information on mutation profiles, including resistant clones, so in that scenario we would favor the metastasis.