The unique feature of HCC is that antecedent chronic hepatitis and liver cirrhosis are common precursor conditions and during transition to malignancy some patients develop autoantibodies which are not present during preceding chronic liver disease phase [
34,
70,
71]. It was shown that novel autoantibodies appeared during conversion to malignancy which were not present in the pre-malignant chronic liver disease phase. In HCC, where novel autoantibody responses are detected during conversion to malignancy, it has been proposed that characterization of the autoantigens driving the novel immune responses might provide insights into intracellular proteins participating in mechanisms leading to malignant transformation [
1]. Many researchers have been interested in the use of autoantibodies as serological markers for cancer diagnosis, especially because of the general absence or a significantly lower frequency of these autoantibodies in normal individuals and in non-cancer conditions [
7,
72]. Enthusiasm for this approach has been tempered by low sensitivity when individual antigen-antibody reactions were studied.
Antibody frequency to any individual TAA was variable but rarely exceeded 15-20% [
7,
73]. We have observed that this drawback can be overcome by using a panel of carefully selected TAAs to achieve the sensitivity and specificity required to make immunodiagnosis a feasible adjunct to tumor diagnosis. This feature is one of the innovative notions in our studies. Previous observations show that antibodies to any individual antigen such as p53 [
7], c-myc [
7,
74], p62 [
7] do not reach levels of sensitivity which could become routinely useful in diagnosis. Wang et al developed a phage-display library derived from prostate cancer tissue, and a phage protein microarray, to analyze autoantibodies in serum samples from patients with prostate cancer and controls [
72]. In this study, a 22-phage-peptide detector was constructed for prostate cancer screening, with 81.6% sensitivity and 88.2% specificity, which indicated that combinations of multiple antigen-antibody systems might acquire higher sensitivity for diagnosis of cancer [
72]. One of our previous studies showed that detection of autoantibodies in cancer can be enhanced by using a mini-array of seven TAAs as target antigens which included c-myc, p53, cyclin B1, p62/IMP2, Koc, IMP1 and survivin [
7,
73]. Antibody frequency to any individual TAA ranged from 10.8 to 24.6% in HCC. With the addition of TAAs to a final total of seven antigens, there was a stepwise increase of positive antibody reactions up to 56.9% in HCC. In our further study, p16, a cyclin-dependent kinase inhibitor, was evaluated as a TAA and added into our previously constituted mini-array of seven TAAs. Antibody frequency to any individual TAA in HCC was variable from 9.9%-21.8% but rarely exceeded 20%. There was a stepwise increase of positive antibody reactions up to 59.9% with successive addition of TAAs to a final of eight antigens, which was significantly higher than the frequency of antibodies in chronic hepatitis (20%), liver cirrhosis (30%) and normal individuals (12.2%). The sensitivity on diagnosing HCC was 59.9%, and the specificity was 87.8%, 80% and 70%, respectively, compared to normal individuals, chronic hepatitis and liver cirrhosis [
75]. The data from our studies indicates that the combination of antibodies might acquire higher sensitivity for diagnosis of cancer.
Nevertheless, in the selection of different antigen-antibody systems, some of the antigens may turn out to be more specific for a certain type of cancer while others may be not. It is conceivable that autoantibody profiles involving different panels or arrays of TAAs might be developed and the results could be useful for diagnosis of certain types of cancer. We stress the notion that panels of “customized” TAAs should be used for different types of tumor and that these customized panels should be rigorously tested for sensitivity and specificity not only against other tumors but also against other diseases conditions. In the case of HCC, the natural conditions could be chronic hepatitis and liver cirrhosis. The basis for the notion of the necessity of customized panels of TAAs is based not only on empirical observations but also on retrospective analysis of our own data learned from previously published work [
7,
34,
71,
73]. The main focus of our studies is to identify a specific panel of TAAs for HCC and compare and contrast this with antigen panels associated with chronic hepatitis and liver cirrhosis.