Pulmonary<unk>  shown on Chest X-Ray The cells in a<unk> astatic tumor resemble those in the primary tumor. Once the cancerous tissue is examined under a microscope to determine the cell type, a doctor can usually tell whether that type of cell is normally found in the part of the body from which the tissue sample was taken. For instance, breast cancer cells look the same whether they are found in the breast or have spread to another part of the body. So, if a tissue sample taken from a tumor in the lung contains cells that look like breast cells, the doctor determines that the lung tumor is a secondary tumor. Still, the determination of the primary tumor can often be very difficult, and the pathologist may have to use several adjuvant techniques, such as immunohistochemistry, FISH (fluorescent in situ hybridization), and others. Despite the use of techniques, in some cases the primary tumor remains unidentified.<unk> astatic cancers may be found at the same time as the primary tumor, or months or years later. When a second tumor is found in a patient that has been treated for cancer in the past, it is more often a<unk>  than another primary tumor. It was previously thought that most cancer cells have a low<unk> astatic potential and that there are rare cells that develop the ability to<unk> e through the development of somatic mutations. According to this theory, diagnosis of<unk> astatic cancers is only possible after the event of<unk> . Traditional means of diagnosing cancer (e.g. a biopsy) would only investigate a subpopulation of the cancer cells and would very likely not sample from the subpopulation with<unk> astatic potential. The somatic mutation theory of<unk>  development has not been substantiated in human cancers. Rather, it seems that the genetic state of the primary tumor reflects the ability of that cancer to<unk> e. Research comparing gene expression between primary and<unk> astatic adenocarcinomas identified a subset of genes whose expression could distinguish primary tumors from<unk> astatic tumors, dubbed a "metastatic signature." Up-regulated genes in the signature include: SNRPF, HNRPAB, DHPS and securin. Actin, myosin and MHC class II down-regulation was also associated with the signature. Additionally, the<unk> astatic-associated expression of these genes was also observed in some primary tumors, indicating that cells with the potential to<unk> e could be identified concurrently with diagnosis of the primary tumor. Recent work identified a form of genetic instability in cancer called chromosome instability (CIN) as a driver of<unk> . In aggressive cancer cells, loose DNA fragments from unstable chromosomes spill in the cytosol leading to the chronic activation of innate immune pathways, which are hijacked by cancer cells to spread to distant organs. Expression of this<unk> astatic signature has been correlated with a poor prognosis and has been shown to be consistent in several types of cancer. Prognosis was shown to be worse for individuals whose primary tumors expressed the<unk> astatic signature. Additionally, the expression of these<unk> astatic-associated genes was shown to apply to other cancer types in addition to adenocarcinoma.<unk>  of breast cancer, medulloblastoma and prostate cancer all had similar expression patterns of these<unk> -associated genes. The identification of this<unk> -associated signature provides promise for identifying cells with<unk> astatic potential within the primary tumor and hope for improving the prognosis of these<unk> astatic-associated cancers. Additionally, identifying the genes whose expression is changed in<unk>  offers potential targets to inhibit<unk> . File:Bone<unk> .Cut surface of a humerus sawn lengthwise, showing a large cancerous<unk>  (the whitish tumor between the head and the shaft of the bone) File:Lymph node with papillary thyroid carcinoma.Micrograph of thyroid cancer (papillary thyroid carcinoma) in a lymph node of the neck. H&E stain File:MultipleLiverMets2008.CT image of multiple liver<unk>  File:LungMets2008.CT image of a lung<unk>  File:Adenocarcinoma liver<unk> .Metastasis proven by liver biopsy (tumor (adenocarcinoma)—lower two-thirds of image). H&E stain. File:MetsToLungs.Metastatic cancer in the lungs File:MetstoBrain(LungPri)Mark.Metastases from the lungs to the brain File:Metstopancrease.Metastases from the lungs to the pancreas
Metastasis
Diastasis 
Gliosis
Mixed tumor
Stoma 
Lymphatogenous metastasis
Vascular tumor
Tumor progression