A method for diagnosing a growth in a subject comprising: (a) analyzing a sample of a growth obtained from thyroid tissue comprising a thyroid nodule by an immunoassay to determine the concentration of midkine protein in the sample, or (a') analyzing a sample of a growth obtained from thyroid tissue comprising a thyroid nodule by an immunoassay to determine the concentration of pleiotrophin protein in the sample, (b) analyzing the sample by an immunoassay to determine the concentration of thyroglobulin protein in the sample, (c) determining the ratio of midkine protein concentration to thyroglobulin protein concentration (MK/Tg) in the sample, or (c') determining the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration (PTN/Tg) in the sample, (d) comparing the ratio of midkine protein concentration to thyroglobulin protein concentration determined from the sample with a control, or (d') comparing the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration determined from the sample with a control, and (e) providing a diagnosis of the growth as a malignant growth after determining an increased ratio of midkine protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, or providing a diagnosis of the growth as a benign growth after determining an equivalent or decreased ratio of midkine protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, wherein the control is the ratio of midkine protein concentration to thyroglobulin protein concentration in a benign growth, or (e') providing a diagnosis of the growth as a malignant growth after determining an increased the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, or providing a diagnosis of the growth as a benign growth after determining an equivalent or decreased ratio of pleiotrophin protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, wherein the control is the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration in a benign growth. (a) analyzing a sample of a growth obtained from thyroid tissue comprising a thyroid nodule by an immunoassay to determine the concentration of midkine protein in the sample, or (a') analyzing a sample of a growth obtained from thyroid tissue comprising a thyroid nodule by an immunoassay to determine the concentration of pleiotrophin protein in the sample, (b) analyzing the sample by an immunoassay to determine the concentration of thyroglobulin protein in the sample, (c) determining the ratio of midkine protein concentration to thyroglobulin protein concentration (MK/Tg) in the sample, or (c') determining the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration (PTN/Tg) in the sample, (d) comparing the ratio of midkine protein concentration to thyroglobulin protein concentration determined from the sample with a control, or (d') comparing the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration determined from the sample with a control, and (e) providing a diagnosis of the growth as a malignant growth after determining an increased ratio of midkine protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, or providing a diagnosis of the growth as a benign growth after determining an equivalent or decreased ratio of midkine protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, wherein the control is the ratio of midkine protein concentration to thyroglobulin protein concentration in a benign growth, or (e') providing a diagnosis of the growth as a malignant growth after determining an increased the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, or providing a diagnosis of the growth as a benign growth after determining an equivalent or decreased ratio of pleiotrophin protein concentration to thyroglobulin protein concentration determined from the sample as compared to the control, wherein the control is the ratio of pleiotrophin protein concentration to thyroglobulin protein concentration in a benign growth.