MicroRNAs expression signature for determination of tumors origin

A method of distinguishing between a primary gastrointestinal (GI) tumor and a GI metastatic tumor, the method comprising:

• (a) providing RNA from a biological sample obtained from a human subject;
• (b) determining an expression profile of nucleic acids consisting of SEQ ID NOS:
• 1 and 4, by contacting the RNA with probes consisting of (i) a first nucleic acid probe, wherein the sequence of the first nucleic acid probe consists of the complement of SEQ ID NO:
• 1 and a linker of 10-60 nucleotides on the 3′ end of the complement of SEQ ID NO:
• 1;
• (ii) a second nucleic acid probe, wherein the sequence of the second nucleic acid probe consists of the complement of SEQ ID NO:
• 4 and a linker of 10-60 nucleotides at the 3′ end of the complement of SEQ ID NO:
• 4;
• and (iii) optionally a control probe;
• wherein the probes are attached to a solid support;
• (c) comparing the expression profile from the biological sample to a reference expression profile;
• and
• (d) distinguishing the biological sample as a primary GI tumor or a GI metastatic tumor based on the comparison of the expression profiles.