Methods for detecting 5T4-positive circulating tumor cells and methods of diagnosis of 5T4-positive cancer in a mammalian subject

A method for detecting 5T4-positive circulating tumor cells in a mammalian subject suspected of having 5T4-positive cancer and treating the mammalian subject comprising:

• obtaining a sample of blood from the mammalian subject;
• testing the sample of blood from the mammalian subject, wherein the sample of blood comprises a cell population;
• mounting the sample of blood on a substrate;
• detecting the presence of a nucleated cell using a first marker in the sample of blood, wherein the first marker is DAPI;
• detecting the presence of expression of a second marker on a circulating tumor cell in the sample of blood, wherein the second marker is cytokeratin;
• detecting the absence of expression of a third marker on a circulating tumor cell in the sample of blood, wherein the third marker is CD45;
• detecting the presence of expression of a fourth marker on a circulating tumor cell in the sample of blood, wherein the fourth marker is human 5T4 antigen;
• analyzing the first, second, third, and fourth markers in the cell population to identify and characterize the circulating tumor cells;
• quantifying the expression of human 5T4 antigen on the circulating tumor cells, assigning an H-score category, and summing the percentage of cells in each H-score category multiplied by the value of the H-score category to generate an H-score, wherein the H-score is used to select a 5T4-positive cancer patient population;
• and
• administering an effective amount of an anti-5T4 antibody-drug conjugate to the mammalian subject in the 5T4-positive cancer patient population.