Preoperative CA19­9 level and dual time point FDG­PET/CT as strong biological indicators of borderline resectability in pancreatic cancer: A retrospective study.

Tumor resectability, which is increasingly determined based on preoperative chemotherapy, is critical in determining the best treatment for pancreatic cancers. The present study evaluated the usefulness of serum carbohydrate antigen 19-9 (CA19-9) and the preoperative 8F-fluorodeoxyglucose positron emission tomography/computed tomography standardized uptake value (SUV) percentage change (SUVmax%=[(SUVmax2-SUVmax1)/SUVmax1] ×100, where SUVmax1 and SUVmax2 represent the initial and delayed phases, respectively) as biological factors indicative of tumor resectability. The present study included patients with resectable pancreatic cancer who underwent complete surgical resection, for whom both CA19-9 and SUVmax% were documented using cut-off values of 500 U/ml and 24.25%, respectively. Patients were classified as follows: i) High CA19-9 and SUVmax%: both CA19-9 and SUVmax% were elevated; ii) high CA19-9 or SUVmax%: either CA19-9 or SUVmax% were elevated; or iii) low CA19-9 and SUVmax%: neither value met the cut-off. Relapse-free survival (RFS) and overall survival (OS) were calculated, for which univariate and multivariate analyses were performed. Of the 86 patients included, 39 were classified as high CA19-9 or SUVmax% and 12 as high CA19-9 and SUVmax%, with the former group having a significantly worse RFS (vs. low CA19-9 and SUVmax%; P<0.001; vs. high CA19-9 or SUVmax%; P=0.011) and OS (vs. low CA19-9 and SUVmax%, P=0.002; vs. high CA19-9 or SUVmax%, P<0.001). Therefore, high CA19-9 and SUVmax% was an independent predictor of worse RFS (P<0.001) and OS (P=0.003). In conclusion, CA19-9 and SUVmax% can be utilized as biological indicators of resectability.

Impact of Preoperative Tumor Size on Prognosis of Resectable and Borderline Resectable Pancreatic Ductal Adenocarcinomas.

BACKGROUND: Tumor size (TS) is a well-established prognostic factor of pancreatic ductal adenocarcinoma (PDAC). However, whether a uniform treatment strategy can be applied for all resectable PDACs (R-PDACs) and borderline resectable PDACs (BR-PDACs), regardless of TS, remains unclear. This study aimed to investigate the impact of preoperative TS on surgical outcomes of patients with R-PDACs and BR-PDACs. METHODS: Chart data from three institutions were reviewed to select patients who underwent pancreatectomy for R-PDACs and BR-PDACs between January 2006 and December 2020. The patients were divided into TSsmall and TSlarge groups according to a TS cutoff value determined for each of R- and BR-PDAC using the minimum P value approach for the risk of R1 resection. RESULTS: TS of 35 mm and 24 mm was the best cutoff value in R-PDAC and BR-PDAC, respectively. The R1 rate was higher in the TSlarge than TSsmall group, in both R- (n = 35, 37% versus n = 294, 19%; P = 0.011) and BR-PDAC (n = 89, 37% versus n = 27, 15%; P = 0.030). Overall survival was significantly better in the TSsmall than TSlarge group in R-PDAC (38.2 versus 12.1 months; P < 0.001), but comparable between the two groups in BR-DPAC (21.2 versus 22.7 months; P = 0.363). Multivariate analysis revealed TS > 35 mm as an independent predictor of worse survival in patients with R-PDAC. CONCLUSION: Larger TS was associated with a higher R1 rate and is a worse prognostic factor in patients with R-PDAC.

Impact of retention index on the neoadjuvant chemotherapy effect and the prognosis in oesophageal cancer.

OBJECTIVE: The relationship between retention index calculated from dual-time point 18F-fluorodeoxyglucose positron emission tomography-computed tomography and oesophageal cancer prognosis remains unknown. This study aimed to determine usefulness of retention index as a predictor of long-term prognosis of oesophageal cancer and neoadjuvant chemotherapy efficacy. METHODS: A total of 151 patients with oesophageal cancer who underwent esophagectomy were evaluated retrospectively in this study. We acquired positron emission tomography scans 60 and 120 min (SUVmax1 and SUVmax2, respectively) after the intravenous administration of 3.7 Mbq/kg 18F-fluorodeoxyglucose. The patients were divided into two groups: high-retention index (retention index ≥29%, 107 patients) and low-retention index (retention index <29%, 44 patients). Retention index was calculated as follows: retention index (%) = [(SUVmax2 - SUVmax1)/SUVmax1] × 100. RESULTS: The overall survival and relapse-free survival rates in the high-retention index group were significantly lower than those in the low-retention index group (P < 0.001). Our multivariate analysis identified that the high-retention index group contained independent risk factors for overall survival (hazard ratio: 2.44, P = 0.009) and relapse-free survival (hazard ratio: 2.61, P = 0.002). The high-retention index group exhibited a lower partial response rate to neoadjuvant chemotherapy evaluated by computed tomography (P < 0.001) and a lower pathological therapeutic effect in the resected specimen (P = 0.019) than the low-retention index group. CONCLUSIONS: The retention index was associated with neoadjuvant chemotherapy responses and long-term prognosis for oesophageal cancer.

Splenic Infarction Associated With Epstein-Barr Virus in an Adult With an Anatomic Anomaly: A Case Report.

Splenic infarction (SI) is often associated with circulatory and hematological diseases and infections. Here, we report a rare case of SI in an adult with infectious mononucleosis (IM) caused by the Epstein-Barr (EB) virus. A 31-year-old male with an unremarkable medical history presented with abdominal pain and fever. Contrast-enhanced computed tomography revealed focal SI. The splenic artery branching from the superior mesenteric artery was <5 mm in diameter. The diagnosis of EB virus infection was made based on physical examination and blood test results. As no evidence of cardiogenic disease, malignant lymphoma, or other infections were present, a diagnosis of SI associated with IM was made. A symptomatic treatment was administered, and the splenomegaly and SI improved two weeks after discharge. IM was assumed as the cause of the focal SI.

Prognostic impact of desmoplastic reaction in esophageal squamous cell carcinoma patients with neoadjuvant therapy.

AIM: This study aimed to examine the prognostic value of desmoplastic reaction (DR) in esophageal squamous cell carcinoma (ESCC), particularly in patients who received neoadjuvant therapy, such as chemotherapy (NAC) or chemoradiotherapy (NACRT). METHOD: In total, 153 patients with pStage II/III ESCC were included in this study. Ninety-one patients received neoadjuvant therapy (NAC, 70; NACRT, 21). Patients were classified according to three DR categories based on the presence of keloid-like collagen and/or myxoid stroma. RESULTS: In total, 50, 50, and 53 patients were classified as having mature, intermediate, and immature DR, respectively. The weighted kappa coefficient was 0.623 in the patients with preoperative treatments and 0.782, in those without. The 5-year disease-specific survival (DSS) rates in patients with intermediate/immature DR was significantly worse than those with mature DR (40.7% vs. 73.3%, p < 0.001). Similarly, the 5-year DSS rate in patients with intermediate/immature DR was significantly worse than those with mature DR in a study of patients who received neoadjuvant therapy (46.7% vs. 71.2%, p = 0.009). Multivariate analysis revealed that DR (hazard ratio [HR]: 3.15, 95% confidence interval [CI] 1.58-6.27, p = 0.001), along with N factors, was an independent risk factor for DSS. Moreover, multivariate analysis of patients who received neoadjuvant therapy revealed only DR (HR: 2.47, 95% CI 1.02-5.96, p = 0.045) as independent risk factors for DSS. CONCLUSION: The DR classification was a valuable prognostic factor not only in the ESCC patients without neoadjuvant therapy but also in those with neoadjuvant therapy.

Periostin derived from cancer-associated fibroblasts promotes esophageal squamous cell carcinoma progression via ADAM17 activation.

Periostin (POSTN) is a matricellular protein that was originally identified in osteoblasts. Past studies have shown that POSTN is also preferentially expressed in cancer-associated fibroblasts (CAFs) in various types of cancer. We previously demonstrated that the increased expression of POSTN in stromal tissues is associated with an unfavorable clinical outcome in esophageal squamous cell carcinoma (ESCC) patients. In this study, we aimed to elucidate the role of POSNT in ESCC progression and its underlying molecular mechanism. We found that POSTN is predominantly produced by CAFs in ESCC tissues, and that CAFs-cultured media significantly promoted the migration, invasion, proliferation, and colony formation of ESCC cell lines in a POSTN-dependent manner. In ESCC cells, POSTN increased the phosphorylation of ERK1/2 and stimulated the expression and activity of a disintegrin and metalloproteinase 17 (ADAM17), which is critically involved in tumorigenesis and tumor progression. The effects of POSTN on ESCC cells were suppressed by interfering with the binding of POSTN to integrin αvß3 or αvß5 using neutralizing antibody against POSTN. Taken together, our data show that CAFs-derived POSTN stimulates ADAM17 activity through activation of the integrin αvß3 or αvß5-ERK1/2 pathway and thereby contributes to the progression of ESCC.

Prognosis of Pancreatic Cancer Based on Resectability: A Single Center Experience.

Although conversion surgery has increasingly been performed for initially unresectable advanced pancreatic ductal adenocarcinoma (PDAC), the rate of conversion, including that for patients who do not undergo resection, remains unclear. Patients with PDAC who were treated between January 2013 and December 2018 were classified into three groups: resectable (R), borderline resectable (BR), and unresectable (UR). We analyzed patient outcomes, including the rate of surgical resection and survival, in each of these groups. In total, 211 patients (R, 118; BR, 22; UR, 81) were selected. Among them, 117 (99%), 18 (82%), and 15 (19%) patients in the R, BR, and UR groups, respectively, underwent surgical resection. R0 resection rates were 88, 78, and 67%, whereas median overall survival (OS) from treatment initiation were 31, 18, and 11 months (p < 0.0001) in the R, BR, and UR groups, respectively. In patients who underwent surgical resection, relapse-free survival (RFS) and OS were similar among the three groups (R vs. BR vs. UR; median RFS (months), 17 vs. 13 vs. 11, p = 0.249; median OS (months), 31 vs. 26 vs. 32, p = 0.742). Lymph node metastases and incomplete adjuvant chemotherapy were identified as independent prognostic factors for OS. Although the surgical resection rate was low, particularly in the BR and UR groups, the prognosis of patients who underwent surgical resection was similar irrespective of the initial resectability status.

Clinical significance of postoperative subcutaneous emphysema after video-assisted thoracoscopic surgery for esophageal cancer.

BACKGROUND: Postoperative subcutaneous emphysema (SE) is a possible complication of thoracoscopic or laparoscopic surgery. This study investigated the risk factors and clinical significance of SE after video-assisted thoracoscopic surgery for esophageal cancer (VATS-e). METHODS: This study included 135 patients who underwent VATS-e with artificial CO2 pneumothorax. Based on the X-ray images on the first postoperative day, patients were divided into two groups: N/L group (no SE or SE localized at the thoracic area, n = 65) and SE group (SE extended to the cervical area, n = 70). We compared clinicopathological features, surgical findings, and short-term outcomes between the two groups. RESULTS: In SE group, there were more patients who received neoadjuvant chemotherapy compared to N/L group. SE group had significantly lower preoperative body mass index. SE group had more frequently two-lung ventilation than N/L group. Multivariate analysis demonstrated that low BMI, NAC, and two-lung ventilation were independent risk factors for SE extended to the cervical area. Although pulmonary complication was relatively frequent in SE group, there were no significant differences in surgical outcomes between two groups, and all patients had SE disappeared within 21 days without serious complications. CONCLUSIONS: Despite extension to the cervical area, SE had a modest impact on the short-term result of VATS-e with artificial CO2 pneumothorax.

Modified Geriatric Nutrition Risk Index as a Prognostic Predictor for Unresectable/Recurrent Esophageal Cancer.

BACKGROUND/AIM: This study aimed to evaluate the prognostic value of modified geriatric nutritional risk index (mGNRI) in patients with unresectable/recurrent esophageal cancer (EC). PATIENTS AND METHODS: We included 143 patients aged >65 years with unresectable/recurrent EC. The mGNRI was calculated as (1.489/CRP in mg/dl) + (41.7 × body mass index/22). Participants were divided into two groups: low-mGNRI (mGNRI <80, n=90) and high-mGNRI (mGNRI ≥80, n=53). We retrospectively examined the relationship between mGNRI and the prognosis of EC. RESULTS: Median survival time in the low-mGNRI group was significantly lower than that in the high-mGNRI group (5.1 vs. 16.9 months, p<0.001). Multivariate analysis revealed that low mGNRI [hazard ratio (HR)=3.85, p<0.001] and absence of chemotherapy or chemoradiotherapy (HR=2.69, p<0.001) were independent and unfavorable prognostic factors of overall survival. Among patients who received chemotherapy or chemoradiotherapy, the mGNRI-low group had a significantly poorer prognosis than the mGNRI-high group (p<0.001). The mGNRI was the most appropriate prognostic index compared with other immune-inflammatory markers by the Akaike and Bayesian information criteria. CONCLUSION: In patients with unresectable/recurrent EC, low mGNRI was correlated with unfavorable prognosis and was a useful independent prognostic factor.

Temperature-controlled laser thermal therapy system using a newly developed laparoscopic system equipped with an ultra-compact thermographic camera.

Laser thermal therapy is one of the treatments for malignant tumors. We developed a thermal endoscope using an ultra-compact thermo-sensor and established a new laparoscopic laser thermal therapy system to heat cancer tissue at an appropriate temperature, focusing on the fact that thermographic cameras are capable of two-dimensional temperature mapping. Hepatocellular carcinoma (N1S1) cells were implanted into the livers of Sprague-Dawley rats (n = 13) to create orthotopic hepatocellular carcinoma. Six of the rats underwent laparoscopic laser thermotherapy (70 °C, 5 min) using the newly developed system, and the others underwent laparoscopic insertion only. Lesion volume measurement and histological evaluation were performed in all of the rats. The laparoscopic laser thermal therapy system provided stable temperature control. When a temperature of 70 °C was used for the set temperature, the temperature of the target cancer was maintained within the range of 68-72 °C for 93.2% of the irradiation time (5 min). The median volume of the tumors that were thermally treated was significantly smaller than that of the untreated tumors. The newly developed laparoscopic laser thermal therapy system was capable of maintaining the temperature of the tumor surface at any desired temperature and was proven to be effective in treatment of the rat hepatocellular carcinoma model.

Enteral versus parental nutrition after pancreaticoduodenectomy under enhanced recovery after surgery protocol: study protocol for a multicenter, open-label randomized controlled trial (ENE-PAN trial).

BACKGROUND: Infectious complications are the main causes of morbidity after pancreaticoduodenectomy (PD). Early enteral nutrition (EN) is a reasonable form of nutritional support that aims to mitigate the occurrence and severity of infectious complications by maintaining gut immunity. However, it remains unclear whether EN is beneficial for patients who underwent PD and are under enhanced recovery after surgery (ERAS) protocol. METHODS: A multicenter (six hospitals), open-label, randomized controlled trial will be started in July 2022. A total of 320 patients undergoing open PD will be randomly assigned to an EN group or a peripheral parental nutrition (PPN) group in a 1:1 ratio. The stratification factors will be the hospital, age (≥ 70 or not), and preoperative diagnosis (pancreatic cancer or not). In the EN group, enteral nutrition will start on postoperative day (POD) 1 at 200-300 ml/day via the percutaneous tube placed operatively. The volume of the diet will be increased to 400-600 ml/day on POD 2 and depend on the surgeon's decision from POD 3. In the PPN group, PPN will be delivered after surgery. In both groups, oral feeding will start on POD 3. Each treatment will be finished when patients' oral food intake reaches 60% of the nutritional requirement (25-30 kcal/day). The primary endpoint will be the occurrence of postoperative infectious complications within 90 days of surgery. The secondary endpoints will be all complications, including major ones such as Clavien-Dindo grade 3 or more and clinically relevant postoperative pancreatic fistula. Data will be analyzed per the intention to treat. DISCUSSION: This will be the first, large, and well-designed RCT that aims to determine whether EN is beneficial for patients who underwent PD under the ERAS protocol. According to the results of this study, either EN or PPN would be adopted as the standard nutritional support for patients undergoing PD. TRIAL REGISTRATION: jRCT1030210691. Registered on March 23, 2022.

Therapeutic efficacy of dose-reduced adjuvant chemotherapy with S-1 in patients with pancreatic cancer: a retrospective study.

BACKGROUND: S-1 adjuvant chemotherapy is the standard treatment in Asia for resectable pancreatic ductal adenocarcinoma. The relative dose intensity of adjuvant chemotherapy influences survival in pancreatic cancer but does not precisely reflect treatment schedule modifications. We investigated the effects of total dose intensity of S-1 adjuvant chemotherapy on the survival of patients with pancreatic cancer and the permissible dose reduction. METHODS: Patients who underwent surgical resection during 2011-2019 for pancreatic cancer were selected. We determined the total dose intensity cut-off value that predicted tumor recurrence within 2 years postoperatively using receiver operating characteristic curves and compared the outcomes between the high and low total dose intensity groups. RESULTS: Patients with total dose intensity ≥ 62.5% (n = 53) showed significantly better overall survival than those with total dose intensity < 62.5% (n = 16) (median survival time: 53.3 vs. 20.2 months, P < 0.001). The median survival of patients without adjuvant chemotherapy (total dose intensity = 0, n = 28) was 24.8 months. Univariate analysis identified lymphatic involvement (P = 0.035), lymph node metastasis (P = 0.034), and total dose intensity (P < 0.001) as factors affecting survival. On multivariate analysis, total dose intensity (P < 0.001) was an independent predictor of worse survival. CONCLUSIONS: Maintaining a total dose intensity of at least 60% in S-1 adjuvant chemotherapy seems important to achieve a long postoperative survival in patients with pancreatic cancer.

Tolerability of neoadjuvant chemotherapy for esophageal cancer in elderly patients over 76 years of age.

Although the Japan Clinical Oncology Group trial demonstrated that neoadjuvant chemotherapy (NAC) with 5-fluorouracil plus cis-diamminedichloroplatinum had significant survival benefits, it excluded elderly patients aged ≥ 76 years. Therefore, our study aimed to evaluate the tolerability of NAC in elderly patients with esophageal cancer. Classified 174 patients with clinical stage II/III esophageal cancer who underwent esophagectomy from 2010 to 2020 into the E (aged ≥ 76 years; 55 patients) and Y (aged < 76; 119 patients) groups, and retrospectively investigated for clinicopathological findings, tolerability of NAC, relative dose intensity (RDI) and short- and long-term result. Patients who received NAC were fewer in the E group than in the Y group (51% vs 77%, p = 0.001). The E group had relatively lower completion rate of NAC (71% vs 85%, p = 0.116) and significantly lower mean RDI of 5-fluorouracil and cis-diamminedichloroplatinum than the Y group (73% vs 89%, p < 0.001). However, histological and radiological were comparable between both groups. Severe adverse events (grade ≥ 3) were relatively frequent (E, 42.9%; Y, 27.5%, p = 0.091), especially, neutropenia was significantly more frequent in the E group (25.0% vs 7.7%, p = 0.022). There were no differences in the incidence of postoperative complications between with and without NAC in both E and Y groups. Elderly patients with esophageal cancer might be more susceptible to toxicity of NAC. Hence, adequate case selection and careful of dose reduction are needed for elderly with esophageal cancer.

Clinical Impact of Dual Time Point 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Fusion Imaging in Pancreatic Cancer.

We examined the value of preoperative dual time point (DTP) 18F-fluorodeoxyglucose positron emission tomography/computed tomography fusion imaging (FDG PET/CT) as a predictor of early recurrence or the outcomes in patients with pancreatic cancer. Standardized uptake values (SUVs) in DTP FDG PET/CT were performed as preoperative staging. SUVmax1 and SUVmax2 were obtained in 60 min and 120 min, respectively. ΔSUVmax% was defined as (SUVmax2 − SUVmax1)/SUVmax1 × 100. The optimal cut-off values for SUVmax parameters were selected based on tumor relapse within 1 year of surgery. Optimal cut-off values for SUVmax1 and ΔSUVmax% were 7.18 and 24.25, respectively. The combination of SUVmax1 and ΔSUVmax% showed higher specificity and sensitivity, and higher positive and negative predictive values for tumor relapse within 1 year than SUVmax1 alone. Relapse-free survival (RFS) was significantly worse in the subgroups of high SUVmax1 and high ΔSUVmax% (median 7.0 months) than in the other subgroups (p < 0.0001). The multivariate Cox analysis of RFS identified high SUVmax1 and high ΔSUVmax% as independent prognostic factors (p = 0.0060). DTP FDG PET/CT may effectively predict relapse in patients with pancreatic cancer. The combination of SUVmax1 and ΔSUVmax% identified early recurrent patient groups more precisely than SUVmax1 alone.

Deep-learning-based classification of desmoplastic reaction on H&E predicts poor prognosis in oesophageal squamous cell carcinoma.

AIMS: Desmoplastic reaction (DR) categorisation has been shown to be a promising prognostic factor in oesophageal squamous cell carcinoma (ESCC). The usual DR evaluation is performed using semiquantitative scores, which can be subjective. This study aimed to investigate whether a deep-learning classifier could be used for DR classification. We further assessed the prognostic significance of the deep-learning classifier and compared it to that of manual DR reporting and other pathological factors currently used in the clinic. METHODS AND RESULTS: From 222 surgically resected ESCC cases, 31 randomly selected haematoxylin-eosin-digitised whole slides of patients with immature DR were used to train and develop a deep-learning classifier. The classifier was trained for 89 370 iterations. The accuracy of the deep-learning classifier was assessed to 30 unseen cases, and the results revealed a Dice coefficient score of 0.81. For survival analysis, the classifier was then applied to the entire cohort of patients, which was split into a training (n = 156) and a test (n = 66) cohort. The automated DR classification had a higher prognostic significance for disease-specific survival than the manually classified DR in both the training and test cohorts. In addition, the automated DR classification outperformed the prognostic accuracy of the gold-standard factors of tumour depth and lymph node metastasis. CONCLUSIONS: This study demonstrated that DR can be objectively and quantitatively assessed in ESCC using a deep-learning classifier and that automatically classed DR has a higher prognostic significance than manual DR and other features currently used in the clinic.

A multicenter phase II trial evaluating the efficacy of bevacizumab plus mFOLFOX6 for R0 surgical resection in advanced colorectal liver metastases harboring mutant-type KRAS: NEXTO-mt trial.

BACKGROUND: The effect of bevacizumab plus mFOLFOX6 on downsizing of liver metastases for curative resection has not been well assessed for patients with advanced colorectal liver metastases (CRLMs). This multicenter phase II trial aimed to examine the efficacy and safety of bevacizumab plus mFOLFOX6 for advanced CRLMs harboring mutant-type KRAS. METHODS: Patients with advanced CRLMs (tumor number of ≥5 and/or technically unresectable) harboring mutant-type KRAS were included. Surgical indication was evaluated every 4 cycles of bevacizumab plus mFOLFOX6. Liver resection was planned if the CRLMs were resectable. The primary endpoint was R0 resection rate. The secondary endpoints included overall survival (OS), recurrence-free survival, progression-free survival, and safety. RESULTS: Between 2013 and 2017, 29 patients from six centers were registered. The rates of complete and partial responses were 0% and 62.1%, respectively. R0 and R1 resections were performed in 19 and 1 patient, respectively (R0 resection rate: 65.5%). No mortality occurred. During the median follow-up of 30.7 months, the 3-year OS rate for all the patients was 64.4% with the median survival of 49.1 months. CONCLUSION: For advanced CRLMs harboring mutant-type KRAS, bevacizumab plus mFOLFOX6 achieved a high R0 resection rate, leading to favorable survival.

Bacterial Translocation in Gastrointestinal Cancers and Cancer Treatment.

In recent years, there has been increasing evidence that gut microbiota is associated with the onset and exacerbation of various diseases, such as gastrointestinal cancer. For instance, it is well known that local inflammation of the intestinal tract in colorectal cancer that is caused by the increased number of Fusobacterium, due to changes in the intestinal bacterial flora, is involved in carcinogenesis. In contrast, gut bacteria or their products, pathogen-associated molecular patterns, not only cause intestinal inflammation but also invade the bloodstream through dysbiosis and gut barrier dysfunction, thereby leading to systemic inflammation, namely bacterial translocation. The involvement of bacterial translocation in the carcinogenesis of gastrointestinal cancers and their prognosis is increasingly being recognized. The Toll-like receptor signaling pathways plays an important role in the carcinogenesis of such cancers. In addition, bacterial translocation influences the treatment of cancers such as surgery and chemotherapy. In this review, we outline the concept of bacterial translocation, summarize the current knowledge on the relationship between gut bacteria and gastrointestinal cancer, and provide future perspectives of this field.