Tissue requirements varied from tissue type to tissue type and from cancer type to cancer type. Disease experts from the project's Disease Working Groups helped to define the characteristics of the typical tissue samples accrued as "standard of care" in the United States and how TCGA can best utilize the tissue. For example, the Brain Disease Working Group determined that samples containing more than 50% necrosis would not be suitable for TCGA and that 80% tumor nuclei were required in the viable portion of the tumor. TCGA followed some general guidelines as a starting point for collecting samples from any type of tumor. These include a minimum of 200 mg in size, no less than 80% tumor nuclei and a matched source of germline DNA (such as blood or purified DNA). In addition, institutions submitting tissues to TCGA must have a minimal clinical data set as defined by the Disease Working Group, signed consents which have been approved by their institution's IRB as well as a material transfer agreement with TCGA.