A Novel Multivariate Index for Pancreatic Cancer Detection Based On the Plasma Free Amino Acid Profile

<div><p>Background</p><p>The incidence of pancreatic cancer (PC) continues to increase in the world, while most patients are diagnosed with advanced stages and survive <12 months. This poor prognosis is attributable to difficulty of early detection. Here we developed and evaluated a multivariate index composed of plasma free amino acids (PFAAs) for early detection of PC.</p><p>Methods</p><p>We conducted a cross-sectional study in multi-institutions in Japan. Fasting plasma samples from PC patients (n = 360), chronic pancreatitis (CP) patients (n = 28), and healthy control (HC) subjects (n = 8372) without apparent cancers who were undergoing comprehensive medical examinations were collected. Concentrations of 19 PFAAs were measured by liquid chromatography–mass spectrometry. We generated an index consisting of the following six PFAAs: serine, asparagine, isoleucine, alanine, histidine, and tryptophan as variables for discrimination in a training set (120 PC and matching 600 HC) and evaluation in a validation set (240 PC, 28 CP, and 7772 HC).</p><p>Results</p><p>Several amino acid concentrations in plasma were significantly altered in PC. Plasma tryptophan and histidine concentrations in PC were particularly low, while serine was particularly higher than that of HC. The area under curve (AUC) based on receiver operating characteristic (ROC) curve analysis of the resulting index to discriminate PC from HC were 0.89 [95% confidence interval (CI), 0.86–0.93] in the training set. In the validation set, AUCs based on ROC curve analysis of the PFAA index were 0.86 (95% CI, 0.84–0.89) for all PC patients versus HC subjects, 0.81 (95% CI, 0.75–0.86) for PC patients from stage IIA to IIB versus HC subjects, and 0.87 (95% CI, 0.80–0.93) for all PC patients versus CP patients.</p><p>Conclusions</p><p>These findings suggest that the PFAA profile of PC was significantly different from that of HC. The PFAA index is a promising biomarker for screening and diagnosis of PC.</p></div

Characteristics of PC patients and healthy controls.

<p>Mann–Whitney U-test (versus HC),</p><p>*<i>p</i> < 0.05;</p><p>***<i>p</i> < 0.001</p><p>^<b>a</b>: Cancer stages were determined according to the Union Internationalis Contra Cancrum (UICC) TNM Classification of Malignant Tumors, 6th Edition.</p><p>^† Chi-square tests to test the differences between PC and HC for categorical data of gender, BMI, and smoking history.</p><p>^‡ Chi-square tests to test the differences between PC and CP for categorical data of gender, BMI, and smoking history.</p><p>Characteristics of PC patients and healthy controls.</p

ROC curves of the PFAA index with different tumor stages, sizes, and locations.

<p>(A) ROC curves of the PFAA index in stage IIA (red), stage IIB (pink), stage III (orange), and stage IV (yellow–green), respectively. (B) ROC curves in TS1 (red), TS2 (pink), TS3 (orange), and TS4 (yellow–green), respectively. TS1 ≤ 2.0 cm, 2.0 cm < TS2 ≤ 4.0 cm, 4.0 cm < TS3 ≤ 6.0 cm, and TS4 > 6.0 cm. (C) ROC curves in the pancreatic head (red), body (pink), and tail (orange), respectively.</p

Discrimination performance of PFAA index.

<p>^<b>a</b>: Following PFAAs was used as variables: Ser, Asn, Ile, Ala, His, and Trp.</p><p>Discrimination performance of PFAA index.</p

ROC curves of the PFAA index of PC patients compared with those of healthy controls in the training set (120 PC and matching 600 HC) (A) and the validation set (240 PC and 7772 HC) (B).

<p>ROC curves of the PFAA index of PC patients compared with those of healthy controls in the training set (120 PC and matching 600 HC) (A) and the validation set (240 PC and 7772 HC) (B).</p

Correlation of PFAA index and other biomarkers (CA19-9, CEA, and elastase 1).

<p>The dotted line shows the cut-off of each biomarker or PFAA index. For data analysis, the upper normal limits of CA19-9, CEA, and elastase-1 were defined as 37 U/mL, 5 ng/dL, and 300 ng/dL, respectively. There were no significant correlations between each biomarker and the PFAA index.</p

Summary of study design and inclusion and exclusion criteria.

<p>Summary of study design and inclusion and exclusion criteria.</p

MIAI for assessing IBD disease activity.

<p>(<b>A</b>) ROCs of the MIAI for discriminating CD and UC patients with active disease and those in remission (Index (CDa/CDr) = 16.474−3.342×[His]−5.190×[Trp]+1.857×[Tau]+2.715×[Met], ROC AUC = 0.894; Index (UCa/UCr) = 34.019−2.926×[Trp]−1.864×[Tyr]−4.777×[Val]−2.856×[Met]+4.604×[Ile], ROC AUC = 0.849). (<b>B</b>) Index (CDa/CDr) cannot discriminate between active disease and remission in UC patients. (<b>C</b>) Correlations between the MIAI and disease activity indexes. Index (CDa/CDr) is correlated with the CDAI (Index = 0.01205×[CDAI]−1.790, r_s = 0.592, p<0.001) and Index (UCa/UCr) is correlated with the CAI (Index = 0.2939×[CAI]−1.433, r_s = 0.598, p<0.001).</p

Spearman's rank correlation coefficients (r_s) for plasma amino acid concentrations.

<p>NS, not significant.</p

Patient characteristics.

<p>Plus-minus values are means±standard deviation.</p