A new tumor marker is being investigated for its usefulness in diagnosing ovarian cancer. A sample of 400 women is stratified into 2 groups based on the presence or absence of BRCA mutations. Serum levels of the new marker are obtained in the 2 groups; in addition, both groups of women undergo conventional screening to determine their disease status. The curves on the top represent the distribution of the new serum marker in women with BRCA mutations, and the curves on the bottom represent the distribution of the new serum marker in women without the BRCA mutations. The proposed serum marker cutoff value for both populations is shown. Use of the new serum marker in women with BRCA mutations, compared with those without BRCA mutations, is associated with which of the following?

Question

A new tumor marker is being investigated for its usefulness in diagnosing ovarian cancer.  A sample of 400 women is stratified into 2 groups based on the presence or absence of BRCA mutations.  Serum levels of the new marker are obtained in the 2 groups; in addition, both groups of women undergo conventional screening to determine their disease status.  The curves on the top represent the distribution of the new serum marker in women with BRCA mutations, and the curves on the bottom represent the distribution of the new serum marker in women without the BRCA mutations.  The proposed serum marker cutoff value for both populations is shown.  Use of the new serum marker in women with BRCA mutations, compared with those without BRCA mutations, is associated with which of the following?

Quizplus · Accepted Answer

11ec160b_3722_0396_9249_a3596e9287e3_MD0001_00 The cutoff value of a quantitative diagnostic test determines whether a given result is interpreted as positive or negative. When there is overlap between the serum values of the healthy and diseased populations, a cutoff value that correctly categorizes all individuals in both populations cannot be chosen. This limits the sensitivity and specificity of the test due to the presence of false positive (FP) and/or false negative (FN) individuals. Sensitivity represents the ability of a test to correctly identify those with a given disease. It is calculated as the number of patients correctly testing positive (TP) divided by the total number of patients with the disease (TP / [TP + FN]). Specificity represents the ability of a test to correctly identify those without a given disease. It is calculated as the number of patients correctly testing negative (TN) divided by the total number of patients without the disease (TN / [TN + FP]). In this case, values of the serum marker in women with BRCA mutations show decreased overlap between the healthy and diseased curves of women with BRCA mutations (curves on the top) compared with women without BRCA mutations (curves on the bottom). The corresponding decrease in the number of FPs and FNs means the new serum marker has higher sensitivity and specificity (ie, better performance) in women with BRCA mutations. Educational objective: The degree of overlap between the healthy and the diseased population curves limits the maximum combined sensitivity and specificity of a quantitative diagnostic test. The degree to which sensitivity or specificity is affected depends on the chosen cutoff value.

A New Tumor Marker Is Being Investigated for Its Usefulness