What does "metastatic signet ring cell adenocarcinoma" mean?

Several things. In this sentence metastatic most likely means the disease has spread to other organs such as liver, lung, etc. And would be considered stage 4; alternatively it could mean spread to lymph nodes only and would represent stage 3 disease. Signet ring is a description of what the cell looks like. Adenocarcinoma is the type of tumor and can arise from the GI tract, prostate, lung, breast or stomach.
Aggressive Cancer. Shahid - without knowing anything else, this is an aggressive cancer. These are descriptive features that we use to understand the biology of the cancer. Signet ring is an aggressive feature. Metastatic means that it is now stage IV - the biopsied specimen is from another tissue, not the place that it was biopsied from. An oncologist should be involved in the care for whoever the patient is.