AminoIndex™ technology was originally developed to screen various types of diseases, such as cancer [1, 7, 15, 16], hepatic or renal failure [17], cardiovascular and metabolic disorders [18–20], and others [21]. The hypothesis for its development was based on the highly sensitive detection of minute changes in metabolic profiles with a focus on PFAA, even if the disease was in the early stages. The AICS™ test is currently performed to detect 7 types of cancers, and the AICS (lung) test for lung cancer is widely used in health and cancer screening in Japan. Several promising studies on similar or the same concepts have been reported abroad [5, 21, 22, 24, 25]. According to our previous findings [1, 8, 9], this test may be an optional tool for the early detection of lung cancer, regardless of the tumor stage or progression, in contrast to other tumor markers, such as serum CEA and CYFRA. However, since the mechanisms responsible for AICS (lung) abnormalities, namely, increases in AICS (lung) values with the occurrence or progression of lung cancer, remain unclear, the usefulness of this test has not yet been examined in detail in clinical practice. For example, clinicopathological differences between patients with and without this AICS (lung) abnormalities remain unclear. We recently reported that AICS (lung) abnormalities in patients with lung cancer may be normalized (from rank C to A or B), when the tumor is completely removed, indicating that AICS (lung) values show some reversibility based on the disease condition [10]. Furthermore, similar findings were reported for other types of cancers [26, 27]. Therefore, changes in amino acid profiles, e.g., AICS values, before and after treatment may be used to predict prognosis and monitor recurrence in patients with several cancers [4, 10, 26, 27].
In the present study, we examined the clinicopathological and prognostic significance of AICS (lung) abnormalities in 297 patients with NSCLC, who underwent curative surgery in our two institutes. The preoperative AICS (lung) status in patients with resectable NSCLC was observed on a relatively large scale: 93 with rank A (31.3%), 82 with rank B (27.7%), and 122 with rank C (41.1%). This distribution was similar to that in our previous study [10]. No relationships were observed between the preoperative AICS (lung) rank and clinicopathological factors, except for patient age and surgical mode. Consistent with previous findings [1, 2, 8, 9], the present results confirmed that AICS (lung) abnormalities was not related to the tumor stage at the start of surgical treatment. Moreover, preoperative o AICS (lung) abnormalities themselves had a significant effect on the frequency of postoperative recurrence among NSCLC patients undergoing curative surgery: patients diagnosed with AICS (lung) rank C in preoperative blood samples showed a significantly higher incidence of tumor recurrence even after complete resection than those diagnosed with the two other ranks. Although a significant impact on OS was not observed, the AICS (lung) rank was associated with the grade of tumor malignancy. This result was more apparent in patients with early-stage disease (p-stage I and II), particularly those with adenocarcinoma. This is the first study to investigate the clinical relationship between the preoperative amino acid profile status and tumor recurrence in and the prognosis of patients with cancer.
In the multivariate analysis, three variables (p-stage, treatment method, and AICS rank) were identified as significant high-risk predictors of tumor recurrence in the present cohort. As described previously [28], the p-stage had the greatest impact on recurrence after curative surgery. It currently remains unclear why the treatment method was regarded as a high-risk predictor; however, a bias was speculated because patients treated with surgery plus adjuvant therapy were intentionally selected as having a high-grade tumor malignancy and potentially unfavorable prognosis in each stage. In contrast, the AICS (lung) rank was firstly suspected to be a confounder associated with the surgical mode. In fact, limited surgery was more selected for rank A + B. Considering that the predictive power of the AICS (lung) rank was mainly limited to a subpopulation of patients with stage I and/or adenocarcinoma, it was also suspected that most patients with adenocarcinoma subtype indicating a predominant ground glass opacity (GGO) on preoperative CT scan image and/or a predominantly lepidic pattern in histology were included in rank A + B. However, such a prognostic good adenocarcinoma subtype was distributed regardless AICS (lung) rank (data not shown). Therefore, the importance of preoperative AICS (lung) abnormalities was clearly determined in a multivariate analysis.
We recently reported that most patients preoperatively diagnosed with rank C potentially exhibited a reduction in the AICS (lung) rank if they were cured after surgery [10]. In contrast, some NSCLC patients without AICS (lung) abnormalities in the preoperative test, namely, those diagnosed with rank A or B, also showed tumor recurrence, even after curative resection. These findings demonstrated that the condition of AICS (lung) abnormalities themselves may not only reflect the tumor-bearing status in patients, but may also be strongly associated with some biological grade of malignant characteristics associated with tumor proliferation, invasiveness, and/or metastasis. However, no significant difference was observed in the clinicopathological factors tested among these ranks. Furthermore, although standard surgery for lung cancer was more frequently performed for rank C, no significant differences were observed in recurrence patterns in the present cohort, suggesting that AICS (lung) abnormalities are not associated with the metastatic route, such as lymphatic, venous, or disseminated spread.
In contrast to the results obtained for RFS, AICS (lung) abnormalities only slightly affected OS. We speculated that this discrepancy was mainly due to some therapeutic effects after recurrence because the predictive value of tumor recurrence was demonstrated in adenocarcinoma. However, typical biomarkers for adenocarcinoma, such as EGFR mutations and ALK abnormalities, were not adequately examined because of the old times of some enrolled patients. The potential relationship between AICS (lung) abnormalities and these therapeutic biomarkers needs to be examined in future studies.
There were some limitations that need to be addressed. Although the number of enrolled patients was relatively large, the predictive value of AICS (lung) abnormalities for tumor recurrence after curative resection was not satisfactory due to the retrospective nature of the analysis. Since its effect on tumor recurrence was limited in patients with early-stage disease and adenocarcinoma, the number of patients was too small to assess its significance. Moreover, the biological mechanisms and condition of AICS (lung) abnormalities in human cancer currently remain unknown. Several amino acids may exert promoting or inhibitory effects on the proliferation of cancer cells [4]. Alanine is regarded as an important key amino acid in apoptosis as well as the proliferation of cancer cells in vitro [4]. Moreover, according to recent findings on novel tissue free amino acid (TFAA) profile analyses [24, 29], the TFAA profile status was strongly associated with malignant characteristics as well as carcinogenesis in cancer patients, and PFAA profiles have been suggested to reflect the status of cancer tissues. Nevertheless, the present study was the first to show that minute changes and/or alterations in PFAA profiles are strongly associated with the biological grade of malignant characteristics. To clarify the predictive significance of AICS (lung) abnormalities on tumor recurrence in NSCLC patients undergoing surgical treatment, not only further validation in other cancers, but also basic research of the underlying mechanisms are warranted.