Regression grading in neoadjuvant treated pancreatic cancer: an interobserver study

Identification of tumour regression in neoadjuvantly treated pancreatic cancer is based on divergent and nonspecific criteria

AIMS

Following the increased use of neoadjuvant therapy for pancreatic cancer, grading of tumour regression (TR) has become part of routine diagnostics. However, it suffers from marked interobserver variation, which is mainly ascribed to the subjectivity of the defining criteria of the categories in TR grading systems. We hypothesized that a further cause for the interobserver variation is the use of divergent and nonspecific morphological criteria to identify tumour regression.

METHODS AND RESULTS

Twenty treatment-naïve pancreatic cancers and 20 pancreatic cancers treated with neoadjuvant chemotherapy were reviewed by three experienced pancreatic pathologists who, blinded for treatment status, categorized each tumour as treatment-naïve or neoadjuvantly treated, and annotated all tissue areas they considered showing tumour regression. Only 50%-65% of the cases were categorized correctly, and the annotated tissue areas were highly discrepant (only 3%-41% overlap). When the prevalence of various morphological features deemed to indicate TR was compared between treatment-naïve and neoadjuvantly treated tumours, only one pattern, characterized by reduced cancer cell density and prominent stroma affecting a large area of the tumour bed, occurred significantly more frequently, but not exclusively, in the neoadjuvantly treated group. Finally, stromal features, both morphological and biological, were investigated as possible markers for tumour regression, but failed to distinguish TR from native tumour stroma.

CONCLUSION

There is considerable divergence in opinion between pathologists when it comes to the identification of tumour regression. Reliable identification of TR is only possible if it is extensive, while lesser degrees of treatment effect cannot be recognized with certainty.

Clinical and pathological factors associated with survival in patients with pancreatic cancer who receive adjuvant therapy after neoadjuvant therapy: A retrospective multi-institutional analysis

BACKGROUND

Neoadjuvant therapy is being increasingly used for patients with pancreatic cancer. The role of adjuvant therapy in these patients is unclear. The purpose of this study was to identify clinical and pathologic characteristics that are associated with longer overall survival in patients with pancreatic cancer who receive adjuvant therapy after neoadjuvant therapy.

METHODS

This study was conducted using multi-institutional data. All patients underwent surgery after at least 1 cycle of neoadjuvant therapy for pancreatic cancer. Patients who died within 3 months after surgery and were known to have distant metastasis or macroscopic residual disease were excluded. Mann-Whitney U test, χ2 analysis, Kaplan-Meier plot, and univariate and multivariate Cox regression analysis were performed as statistical analyses.

RESULTS

In the present study, 529 patients with resected pancreatic cancer after neoadjuvant therapy were reviewed. For neoadjuvant therapy, 177 (33.5%) patients received neoadjuvant chemotherapy, and 352 (66.5%) patients received neoadjuvant chemoradiotherapy. The median duration of neoadjuvant therapy was 7.0 months (interquartile range, 5.0-8.7). Patients were followed for a median of 23.0 months after surgery. Adjuvant therapy was administered to 297 (56.1%) patients and was not associated with longer overall survival for the entire cohort (24 vs 22 months, P = .31). Interaction analysis showed that adjuvant therapy was associated with longer overall survival in patients who received less than 4 months neoadjuvant therapy (hazard ratio 0.40; 95% confidence interval 0.17-0.95; P = .03) or who had microscopic margin positive surgical resections (hazard ratio 0.56; 95% confidence interval 0.33-0.93; P = .03).

CONCLUSION

In this retrospective study, there was a survival benefit associated with adjuvant therapy for patients who received less than 4 months of neoadjuvant therapy or had microscopic positive margins.

[Histopathologic diagnosis of solid and cystic pancreatic lesions with a focus on ductal adenocarcinoma : A vademecum for daily practice]

Pancreas pathology is constantly evolving and can present various challenges for pathologists. This paper is focused on providing helpful hints for daily routine diagnostics. During histopathological analysis of pancreas biopsies, pancreatic ductal adenocarcinoma must be distinguished not only from other solid neoplasms, but especially from its mimicker, autoimmune pancreatitis. This can be achieved by a systematic workup following clear diagnostic criteria. When analyzing samples from cystic pancreatic lesions, mucin-producing neoplasms must be detected due to their role as pancreatic cancer precursors; molecular analyses can help considerably with their detection and distinction. During frozen section examination, evaluation of the pancreatic neck margin and analysis of unclear lesions of the liver are two important tasks, which are explained further in this article. A special challenge is the evaluation of neoadjuvant treated pancreatic cancer, which requires a detailed macroscopic and microscopic workup. Finally, current advances in precision oncology and emerging approaches for pancreatic cancer within this field are discussed. With the advancement of technical possibilities and their increasingly broad implementation, the classification systems in pancreatic pathology will continue to gain in complexity, but also in accuracy.

Artificial intelligence with magnetic resonance imaging for prediction of pathological complete response to neoadjuvant chemoradiotherapy in rectal cancer: A systematic review and meta-analysis

Purpose

The purpose of this study was to evaluate the diagnostic accuracy of artificial intelligence (AI) models with magnetic resonance imaging(MRI) in predicting pathological complete response(pCR) to neoadjuvant chemoradiotherapy (nCRT) in patients with rectal cancer. Furthermore, assessed the methodological quality of the models.

Methods

We searched PubMed, Embase, Cochrane Library, and Web of science for studies published before 21 June 2022, without any language restrictions. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) and Radiomics Quality Score (RQS) tools were used to assess the methodological quality of the included studies. We calculated pooled sensitivity and specificity using random-effects models, I² values were used to measure heterogeneity, and subgroup analyses to explore potential sources of heterogeneity.

Results

We selected 21 papers for inclusion in the meta-analysis from 1562 retrieved publications, with a total of 1873 people in the validation groups. The meta-analysis showed that AI models based on MRI predicted pCR to nCRT in patients with rectal cancer: a pooled area under the curve (AUC) 0.91 (95% CI, 0.88-0.93), sensitivity of 0.82(95% CI,0.71-0.90), pooled specificity 0.86(95% CI,0.80-0.91). In the subgroup analysis, the pooled AUC of the deep learning(DL) model was 0.97, the pooled AUC of the radiomics model was 0.85; the pooled AUC of the combined model with clinical factors was 0.92, and the pooled AUC of the radiomics model alone was 0.87. The mean RQS score of the included studies was 10.95, accounting for 30.4% of the total score.

Conclusions

Radiomics is a promising noninvasive method with high value in predicting pathological response to nCRT in patients with rectal cancer. DL models have higher predictive accuracy than radiomics models, and combined models incorporating clinical factors have higher diagnostic accuracy than radiomics models alone. In the future, prospective, large-scale, multicenter investigations using radiomics approaches will strengthen the diagnostic power of pCR.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/, identifier CRD42021285630.

The Histopathology of Neoadjuvant-Treated (NAT) Pancreatic Ductal Adenocarcinoma

Examination of pancreatic ductal adenocarcinoma after NAT with the intent of diagnosis and outcome prediction remains a challenging task. The lack of a uniform approach to macroscopically assess these cases along with variations in sampling adds to the complexity. Several TRG systems have been proposed to correlate with an overall survival. In clinical practice, most of these TRG schemes have shown low level of interobserver agreement arguing for a need of larger studies and more innovative ways to assess outcome in this population.

Histological tumor necrosis in pancreatic cancer after neoadjuvant therapy

The pathological prognostic factors in pancreatic cancer patients who have received neoadjuvant therapy (NAT) are still elusive. The aim of the present study was to investigate the prognostic potential of histological tumor necrosis (HTN) in patients who received NAT and to evaluate tumor changes after NAT. HTN was studied in 44 pancreatic cancer patients who received NAT followed by surgery (NAT group) compared with 263 patients who received upfront surgery (UFS group). The prognostic factors in the NAT group were analyzed, and carbonic anhydrase 9 (CA‑9) expression was compared between the NAT and USF group to evaluate the hypoxic microenvironment changes during NAT. HTN was found in 15 of 44 patients in the NAT group, and its frequency was lower than that in the UFS group (34 vs. 51%, P=0.04). Cox proportional hazards models identified HTN as an independent risk factor for relapse‑free survival in the NAT group [risk ratio (RR), 5.60; 95% confidence interval (CI): 2.27‑14.26, P<0.01]. Significant correlations were found between HTN and CA‑9 expression both in the NAT and UFS groups (P<0.01 for both). CA‑9 expression was significantly upregulated in the NAT group overall, although this upregulation was specifically induced in patients without HTN. In conclusion, HTN was a poor prognostic factor in pancreatic cancer patients receiving NAT followed by surgery, and the present study suggests a close association between HTN and tumor hypoxia. Increased hypoxia after NAT may support the thesis for re‑engineering the hypoxia‑alleviating tumor microenvironment in NAT regimens for pancreatic cancer.

Pathologic Examination of Pancreatic Specimens Resected for Treated Pancreatic Ductal Adenocarcinoma: Recommendations From the Pancreatobiliary Pathology Society

Currently, there are no internationally accepted consensus guidelines for pathologic evaluation of posttherapy pancreatectomy specimens. The Neoadjuvant Therapy Working Group of Pancreatobiliary Pathology Society was formed in 2018 to review grossing protocols, literature, and major issues and to develop recommendations for pathologic evaluation of posttherapy pancreatectomy specimens. The working group generated the following recommendations: (1) Systematic and standardized grossing and sampling protocols should be adopted for pancreatectomy specimens for treated pancreatic ductal adenocarcinoma (PDAC). (2) Consecutive mapping sections along the largest gross tumor dimension are recommended to validate tumor size by histology as required by the College of American Pathologists (CAP) cancer protocol. (3) Tumor size of treated PDACs should be measured microscopically as the largest dimension of tumor outer limits that is bound by viable tumor cells, including intervening stroma. (4) The MD Anderson grading system for tumor response has a better correlation with prognosis and better interobserver concordance among pathologists than does the CAP system. (5) A case should not be classified as a complete response unless the entire pancreas, peripancreatic tissues, ampulla of Vater, common bile duct, and duodenum adjacent to the pancreas are submitted for microscopic examination. (6) Future studies on tumor response of lymph node metastases, molecular and/or immunohistochemical markers, as well as application of artificial intelligence in grading tumor response of treated PDAC are needed. In summary, systematic, standardized pathologic evaluation, accurate tumor size measurement, and reproducible tumor response grading to neoadjuvant therapy are needed for optimal patient care. The criteria and discussions provided here may provide guidance towards these goals.

Tumor Size Differences Between Preoperative Endoscopic Ultrasound and Postoperative Pathology for Neoadjuvant-Treated Pancreatic Ductal Adenocarcinoma Predict Patient Outcome

BACKGROUND & AIMS

The assessment of therapeutic response after neoadjuvant treatment and pancreatectomy for pancreatic ductal adenocarcinoma (PDAC) has been an ongoing challenge. Several limitations have been encountered when employing current grading systems for residual tumor. Considering endoscopic ultrasound (EUS) represents a sensitive imaging technique for PDAC, differences in tumor size between preoperative EUS and postoperative pathology after neoadjuvant therapy were hypothesized to represent an improved marker of treatment response.

METHODS

For 340 treatment-naïve and 365 neoadjuvant-treated PDACs, EUS and pathologic findings were analyzed and correlated with patient overall survival (OS). A separate group of 200 neoadjuvant-treated PDACs served as a validation cohort for further analysis.

RESULTS

Among treatment-naïve PDACs, there was a moderate concordance between EUS imaging and postoperative pathology for tumor size (r = 0.726, P < .001) and AJCC 8th edition T-stage (r = 0.586, P < .001). In the setting of neoadjuvant therapy, a decrease in T-stage correlated with improved 3-year OS rates (50% vs 31%, P < .001). Through recursive partitioning, a cutoff of ≥47% tumor size reduction was also found to be associated with improved OS (67% vs 32%, P < .001). Improved OS using a ≥47% threshold was validated using a separate cohort of neoadjuvant-treated PDACs (72% vs 36%, P < .001). By multivariate analysis, a reduction in tumor size by ≥47% was an independent prognostic factor for improved OS (P = .007).

CONCLUSIONS

The difference in tumor size between preoperative EUS imaging and postoperative pathology among neoadjuvant-treated PDAC patients is an important prognostic indicator and may guide subsequent chemotherapeutic management.

Reproducibility and prognostic significance of area of residual tumor (ART) in post-neoadjuvant resections of pancreatic ductal adenocarcinoma

BACKGROUND

The pathologic assessments of tumor response after neoadjuvant chemoradiotherapy (NACRT) are critical to improving the prognostic stratification for patients with pancreatic ductal adenocarcinoma (PDAC). Here we clarified the utility of our new grading system based on the area of residual tumor (ART) as compared to existing systems, such as the College of American Pathologists (CAP) and MD Anderson (MDA) score.

METHODS

Eight reviewers individually evaluated the tumor regression grade of 30 patients with PDAC based on three types of grading systems. The interobserver concordance and clinicopathological characteristics were compared between the three systems.

RESULTS

The interobserver concordance (kappa value) of the ART, CAP, and MDA score were 0.61, 0.48, and 0.53, respectively. Discrepant cases, which were 27% of the cases, exhibited smaller tumor and tumor bed sizes than concordant cases. The reduction in tumor size evaluated by microscopy showed a correlation with the rate of change in carcinoembryonic antigen (CEA) level, CA19-9 level, and tumor size on computed tomography (CT). The ART score was correlated with the tumor size on CT before and after NACRT and disease-free survival. The CAP and MDA scores were not associated with prognosis.

CONCLUSION

The ART grading system may be the most practical system to assess the tumor response in post-NACRT resections of PDAC.

Isotoxic high-dose stereotactic body radiotherapy integrated in a total multimodal neoadjuvant strategy for the treatment of localized pancreatic ductal adenocarcinoma

BACKGROUND

Our aim was to evaluate the feasibility and safety of isotoxic high-dose (iHD) stereotactic body radiation therapy (SBRT) in a total neoadjuvant sequence for the treatment of localized pancreatic adenocarcinoma.

MATERIALS AND METHODS

Biopsy-proven borderline resectable/locally advanced pancreatic cancer (BR/LAPC) patients were included in this observational prospective analysis from August 2017 to April 2020 without excluding tumours showing a radiological direct gastrointestinal (GI) invasion. An induction chemotherapy by modified fluorouracil, irinotecan and oxaliplatin was performed for a median of six cycles. In case of non-progression, an isotoxic high-dose stereotactic body radiotherapy (iHD-SBRT) was delivered in 5 fractions followed by a surgical exploration. The primary endpoint was acute/late gastrointestinal grade ⩾3 toxicity. Secondary endpoints were overall survival (OS), progression-free survival (PFS) and local control (LC).

RESULTS

A total of 39 consecutive patients (21 BR and 18 LAPC) were included: 34 patients (87.2%, 18 BR and 16 LAPC) completed the planned neoadjuvant sequence. After iHD-SBRT, 19 patients [55.9% overall, 13/18 BR (72.2%) and 6/16 LAPC (37.5%)] underwent an oncological resection among the 25 patients surgically explored (73.5%). The median follow up was 18.2 months. The rates of acute and late GI grade 3 toxicity were, respectively, 2.9% and 4.2%. The median OS and PFS from diagnosis were, respectively, 24.5 and 15.6 months. The resected patients had improved median OS and PFS in comparison with the non-resected patients (OS: 32.3 versus 18.2 months, p = 0.02; PFS: 24.1 versus 7.1 months, p < 0.001). There was no survival difference between the BR and LAPC patients. The 1-year LC from SBRT was 74.1% and the median locoregional PFS was not reached for both BR and LAPC patients.

CONCLUSIONS

iHD-SBRT displays an excellent toxicity profile, also for potentially high-risk patients with radiological direct GI invasion at diagnosis and can be easily integrated in a total neoadjuvant strategy. The oncological outcomes are promising and emphasise the need for further exploration of iHD-SBRT in phase II/III trials.

Dataset for the reporting of carcinoma of the exocrine pancreas: recommendations from the International Collaboration on Cancer Reporting (ICCR)

BACKGROUND AND OBJECTIVES

Current guidelines for the pathology reporting on pancreatic cancer differ in certain aspects, resulting in divergent reporting practice and a lack of comparability of data. Here we report on a new international dataset for the pathology reporting of resection specimens with cancer of the exocrine pancreas (ductal adenocarcinoma and acinar cell carcinoma). The dataset was produced under the auspices of the International Collaboration on Cancer Reporting (ICCR), a global alliance of major (inter-)national pathology and cancer organisations.

METHODS AND RESULTS

According to the ICCR's rigorous process for dataset development, an international expert panel consisting of pancreatic pathologists, a pancreatic surgeon and an oncologist produced a set of core and non-core data items based on a critical review and discussion of current evidence. Commentary was provided for each data item to explain the rationale for selecting it as a core or non-core element, its clinical relevance, and to highlight potential areas of disagreement or lack of evidence, in which case a consensus position was formulated. Following international public consultation, the document was finalised and ratified, and the dataset, which includes a synoptic reporting guide, was published on the ICCR website.

CONCLUSIONS

This first international dataset for cancer of the exocrine pancreas is intended to promote high quality, standardised pathology reporting. Its widespread adoption will improve consistency of reporting, facilitate multidisciplinary communication and enhance comparability of data, all of which will help to improve the management of pancreatic cancer patients.

Pathology of Treated Pancreatic Ductal Adenocarcinoma and Its Clinical Implications

CONTEXT.—

Preoperative neoadjuvant therapy has been increasingly used to treat patients with potentially resectable pancreatic ductal adenocarcinoma (PDAC). Neoadjuvant therapy often induces extensive fibrosis in tumor, adjacent pancreatic parenchyma, and peripancreatic tissue. Histopathologic evaluations and histologic tumor response grading (HTRG) of posttherapy pancreatectomy specimens are very difficult and challenging. Studies on prognostic significance of posttherapy pathologic staging, optimal system for HTRG, and other pathologic parameters in treated PDAC patients are limited.

OBJECTIVE.—

This review is to provide a timely update of the prognostic values of posttherapy pathologic staging, HTRG, and other pathologic parameters in PDAC patients who received neoadjuvant therapy and pancreas resection.

DATA SOURCES.—

Systemic review of major studies on pathologic evaluation and its clinicopathologic implications in treated PDAC patients.

CONCLUSIONS.—

Systemic pathologic examination, histologic tumor regression grading, pathologic evaluation of the margins, tumor involvement of superior mesenteric vein/portal vein, accurate pathologic staging, and reporting of posttherapy pancreatectomy specimens provide highly valuable prognostic information for postoperative patient care. Our findings suggest for the first time that tumor size of 1.0 cm, instead of 2.0 cm, is a better cutoff for ypT2 in PDAC patients. The newly proposed 3-tier MD Anderson HTRG system not only has proved to be an independent prognostic marker for PDAC patients who received neoadjuvant therapy and pancreatectomy, but also improves interobserver agreement among pathologists in evaluation of tumor response. This grading system should be considered in future editions of the College of American Pathologists protocol for PDAC.

Comparison of Clinical Outcomes of Borderline Resectable Pancreatic Cancer According to the Neoadjuvant Chemo-Regimens: Gemcitabine versus FOLFIRINOX

Background/Aims

Although many studies have reported the promising effect of neoadjuvant treatment for borderline resectable pancreatic cancer (BRPC) to increase resectability, only a few studies have recommended the use of first-line chemotherapeutic agents as neoadjuvant treatment for BRPC. The current study compared clinical outcomes between gemcitabine and FOLFIRINOX (5-fluorouracil, leucovorin, oxaliplatin, and irinotecan) in patients with BRPC.

Methods

In this single-center retrospective study, 100 BRPC patients treated with neoadjuvant chemotherapy and resection from 2008 to 2018 were reviewed. Clinical outcomes included overall survival, resectability, and recurrence patterns after gemcitabine or FOLFIRINOX treatment.

Results

For neoadjuvant chemotherapy, gemcitabine was administered to 34 patients and FOLFIRINOX to 66. Neoadjuvant radiotherapy was administered to 27 patients (79.4%) treated with gemcitabine and 19 (28.8%) treated with FOLFIRINOX (p<0.001). The 2- and 5-year survival rates (YSRs) were significantly higher after FOLFIRINOX (2YSR, 72.2%; 5YSR, 46.0%) than after gemcitabine (2YSR, 58.4%; 5YSR, 19.1%; p=0.041). The margin negative rate was comparable (gemcitabine, 94.1%; FOLFIRINOX, 92.4%; p=0.753), and the tumor size change in percentage showed only a marginal difference (gemcitabine, 20.5%; FOLFIRINOX, 29.0%; p=0.069). Notably, the metastatic recurrence rate was significantly lower in the FOLFIRINOX group (n=20, 52.6%) than in the gemcitabine group (n=22, 78.6%; p=0.001). The rate of adverse events after chemotherapy was significantly higher with FOLFIRINOX than with gemcitabine (43.9%, 20.6%, respectively; p=0.037).

Conclusions

FOLFIRINOX provided more clinical and oncological benefit than gemcitabine, with significantly higher overall survival and lower cumulative recurrence rates in BRPC. However, since FOLFIRINOX causes more adverse effects, the regimen should be individualized based on patient's general condition and clinical status.

Impact of histological response after neoadjuvant therapy on podocalyxin as a prognostic marker in pancreatic cancer

Podocalyxin overexpression associates with poor survival in pancreatic cancer (PDAC). We investigated whether podocalyxin expression correlates with treatment response or survival in neoadjuvant-treated PDAC. Through immunohistochemistry, we evaluated podocalyxin expression in 88 neoadjuvant and 143 upfront surgery patients using two antibodies. We developed a six-tier grading scheme for neoadjuvant responses evaluating the remaining tumor cells in surgical specimens. Strong podocalyxin immunopositivity associated with poor survival in the patients responding poorly to the neoadjuvant treatment (HR 4.16, 95% CI 1.56–11.01, p = 0.004), although neoadjuvant patients exhibited generally low podocalyxin expression (p = 0.017). Strong podocalyxin expression associated with perineural invasion (p = 0.003) and lack of radiation (p = 0.036). Two patients exhibited a complete neoadjuvant response, while a strong neoadjuvant response (≤ 5% of residual tumor cells) significantly associated with lower stage, pT-class and grade, less spread to the regional lymph nodes, less perineural invasion, and podocalyxin negativity (p < 0.05, respectively). A strong response predicted better survival (HR 0.28, 95% CI 0.09–0.94, p = 0.039). In conclusion, strong podocalyxin expression associates with poor survival among poorly responding neoadjuvant patients. A good response associates with podocalyxin negativity. A strong response associates with better outcome.

Four-Tier Pathologic Tumor Regression Grading System Predicts the Clinical Outcome in Patients Who Undergo Surgical Resection for Locally Advanced Pancreatic Cancer after Neoadjuvant Chemotherapy

Background/Aims

Neoadjuvant chemotherapy is increasingly utilized in patients with borderline or locally advanced pancreatic cancer (LAPC). However, the pathologic evaluation of tumor regression is not routinely performed or well established. We aimed to evaluate the prognostic value of three tumor regression grading systems frequently used in LAPC and to determine the correlation between pathologic and clinical response.

Methods

We included a total of 38 patients with LAPC who were treated with neoadjuvant chemotherapy and subsequent resection. Pathologic tumor regression was graded based on the College of American Pathologists (CAP), Evans, and MD Anderson grading systems.

Results

One out of 38 patients (2.6%) achieved a pathologic complete response. Unlike other grading systems (Evans, p=0.063; MD Anderson, p=0.110), the CAP grading system was a significant prognostic factor for overall survival (p=0.043). Pathologic N stage (p=0.023), margin status (p=0.044), and radiologic response (p=0.016) correlated with overall survival. In the multivariate analysis, CAP 3 was an independent predictor of shorter overall survival (p=0.026). The CAP grading system correlated with the radiologic response (p=0.007) but not the carbohydrate antigen 19-9 level (p=0.333).

Conclusions

The four-tier CAP pathologic tumor regression grading system predicted the clinical outcome in LAPC patients who underwent resection after neoadjuvant chemotherapy. Therefore, a more comprehensive pathologic evaluation is warranted in these patients.

A Critical Assessment of Postneoadjuvant Therapy Pancreatic Cancer Regression Grading Schemes With a Proposal for a Novel Approach

Currently, there is no consensus on the optimal tumor response score (TRS) system to assess regression in pancreatic cancers resected after neoadjuvant therapy. We developed a novel TRS (Royal North Shore [RNS] system) based on estimating the percentage of tumor bed occupied by viable cancer and categorized into 3 tiers: grade 1 (≤10%), grade 2 (11% to 75%), and grade 3 (>75%). We assessed 147 resected carcinomas with this and other TRS systems (College of American Pathologists [CAP], MD Anderson Cancer Center [MDACC], and Evans). The 3-tiered RNS system predicted median survival after surgery for grades 1, 2, and 3 of 54, 23, and 9 months, respectively (P<0.05). The CAP, MDACC, and Evans systems also predicted survival (P<0.05) but less consistently. The median survival for MDACC and CAP grade 0 (complete regression) was less than MDACC grade 1 and CAP grades 1 and 2. There was no difference in survival between CAP grades 2 and 3 (P=0.960), Evans grades 1 and 2a (P=0.395), and Evans grades 2a and 2b (P=0.587). Interobserver concordance was weak for CAP (κ=0.431), moderate for MDACC (κ=0.691), minimal for Evans (κ=0.307), and moderate to strong for RNS (κ=0.632 to 0.84). Of age, sex, size, stage, grade, perineural and vascular invasion, extrapancreatic extension, margin status, and RNS score, only RNS score, vascular invasion, and extrapancreatic extension predicted survival in univariate analysis. Only extrapancreatic extension (P=0.034) and RNS score (P<0.0001) remained significant in multivariate analysis. We conclude that the RNS system is a reproducible and powerful predictor of survival after resection for pancreatic cancers treated with neoadjuvant therapy and should be investigated in larger cohorts.

Scoring of tumour response after neoadjuvant therapy in resected pancreatic cancer: systematic review

BACKGROUND

Preoperative chemo(radio)therapy is used increasingly in pancreatic cancer. Histological evaluation of the tumour response provides information on the efficacy of preoperative treatment and is used to determine prognosis and guide decisions on adjuvant treatment. This systematic review aimed to provide an overview of the current evidence on tumour response scoring systems in pancreatic cancer.

METHODS

Studies reporting on the assessment of resected pancreatic ductal adenocarcinoma following neoadjuvant chemo(radio)therapy were searched using PubMed and EMBASE. All original studies reporting on histological tumour response in relation to clinical outcome (survival, recurrence-free survival) or interobserver agreement were eligible for inclusion. This systematic review followed the PRISMA guidelines.

RESULTS

The literature search yielded 1453 studies of which 25 met the eligibility criteria, revealing 13 unique scoring systems. The most frequently investigated tumour response scoring systems were the College of American Pathologists system, Evans scoring system, and MD Anderson Cancer Center system, investigated 11, 9 and 5 times respectively. Although six studies reported a survival difference between the different grades of these three systems, the reported outcomes were often inconsistent. In addition, 12 of the 25 studies did not report on crucial aspects of pathological examination, such as the method of dissection, sampling approach, and amount of sampling.

CONCLUSION

Numerous scoring systems for the evaluation of tumour response after preoperative chemo(radio)therapy in pancreatic cancer exist, but comparative studies are lacking. More comparative data are needed on the interobserver variability and prognostic significance of the various scoring systems before best practice can be established.

Morphologic changes associated with neoadjuvant-treated pancreatic ductal adenocarcinoma and comparison of two tumor regression grading systems

Pancreatic ductal adenocarcinoma (PDAC) is aggressive, with an overall five-year survival rate of 9%, and few patients are candidates for pancreatectomy at presentation. The role of neoadjuvant therapy (NAT) is evolving, especially for high-risk potentially resectable tumors. Owing to the increasing number of NAT resection specimens, we aim to characterize the histologic changes associated with NAT and to compare two tumor regression grading schemes. One hundred eighteen resections for PDAC were selected from the cases between 2011 and 2018, 59 not treated and 59 treated with NAT. All H&E stained tumor slides were reviewed for histologic changes and graded using the four-tier modified Ryan score (recommended by College of American Pathologists) and the three-tier MD Anderson (MDA) score. The histologic changes evaluated included blue/grey fibrosis, islet cell hyperplasia, dystrophic calcification, amyloid deposition, cholesterol clefts, nerve hypertrophy, elastotic stromal/vascular change, abscess formation, and eosinophilic tumor cell changes. There were statistically significant differences for dystrophic calcification, eosinophilic tumor cell changes, elastotic stromal/vascular change, islet cell hyperplasia, and nerve hypertrophy between the two groups, with these features seen more frequently in NAT cases. Blue/grey stromal fibrosis was present in all cases regardless of NAT, except few complete regression cases and one treated case with intraneural invasion only. Blue/grey fibrosis is a useful histologic visual clue to suggest the possibility of adjacent tumor in the majority of PDAC cases regardless of NAT. By Kaplan-Meier analysis, neither grading scheme correlated with overall survival in our cohort. However, the MDA score was significantly correlated with both time to primary tumor recurrence (p = 0.002) and time to distant recurrence (p = 0.04), whereas the modified Ryan score was not.

Amsterdam International Consensus Meeting: tumor response scoring in the pathology assessment of resected pancreatic cancer after neoadjuvant therapy

Histopathologically scoring the response of pancreatic ductal adenocarcinoma (PDAC) to neoadjuvant treatment can guide the selection of adjuvant therapy and improve prognostic stratification. However, several tumor response scoring (TRS) systems exist, and consensus is lacking as to which system represents best practice. An international consensus meeting on TRS took place in November 2019 in Amsterdam, The Netherlands. Here, we provide an overview of the outcomes and consensus statements that originated from this meeting. Consensus (≥80% agreement) was reached on a total of seven statements: (1) TRS is important because it provides information about the effect of neoadjuvant treatment that is not provided by other histopathology-based descriptors. (2) TRS for resected PDAC following neoadjuvant therapy should assess residual (viable) tumor burden instead of tumor regression. (3) The CAP scoring system is considered the most adequate scoring system to date because it is based on the presence and amount of residual cancer cells instead of tumor regression. (4) The defining criteria of the categories in the CAP scoring system should be improved by replacing subjective terms including "minimal" or "extensive" with objective criteria to evaluate the extent of viable tumor. (5) The improved, consensus-based system should be validated retrospectively and prospectively. (6) Prospective studies should determine the extent of tissue sampling that is required to ensure adequate assessment of the residual cancer burden, taking into account the heterogeneity of tumor response. (7) In future scientific publications, the extent of tissue sampling should be described in detail in the "Materials and methods" section.

Objective assessment of tumor regression in post-neoadjuvant therapy resections for pancreatic ductal adenocarcinoma: comparison of multiple tumor regression grading systems

Neoadjuvant therapy is increasingly used to control local tumor spread and micrometastasis of pancreatic ductal adenocarcinoma (PDAC). Pathology assessments of treatment effects might predict patient outcomes after surgery. However, there are conflicting reports regarding the reproducibility and prognostic performance of commonly used tumor regression grading systems, namely College of American Pathologists (CAP) and Evans' grading system. Further, the M.D. Anderson Cancer Center group (MDA) and the Japan Pancreas Society (JPS) have introduced other grading systems, while we recently proposed a new, simple grading system based on the area of residual tumor (ART). Herein, we aimed to assess and compare the reproducibility and prognostic performance of the modified ART grading system with those of the four grading systems using a multicenter cohort. The study cohort consisted of 97 patients with PDAC who had undergone post-neoadjuvant pancreatectomy at four hospitals. All patients were treated with gemcitabine and S-1 (GS)-based chemotherapies with/without radiation. Two pathologists individually evaluated tumor regression in accordance with the CAP, Evans', JPS, MDA and ART grading systems, and interobserver concordance was compared between the five systems. The ART grading system was a 5-tiered system based on a number of 40× microscopic fields equivalent to the surface area of the largest ART. Furthermore, the final grades, which were either the concordant grades of the two observers or the majority grades, including those given by the third observer, were correlated with patient outcomes in each system. The interobserver concordance (kappa value) for Evans', CAP, MDA, JPS and ART grading systems were 0.34, 0.50, 0.65, 0.33, and 0.60, respectively. Univariate analysis showed that higher ART grades were significantly associated with shorter overall survival (p = 0.001) and recurrence-free survival (p = 0.005), while the other grading systems did not show significant association with patient outcomes. The present study revealed that the ART grading system that was designed to be simple and more objective has achieved high concordance and showed a prognostic value; thus it may be most practical for assessing tumor regression in post-neoadjuvant resections for PDAC.

Borderline Resectable and Locally Advanced Pancreatic Cancer: FDG PET/MRI and CT Tumor Metrics for Assessment of Pathologic Response to Neoadjuvant Therapy and Prediction of Survival

BACKGROUND. Imaging biomarkers of response to neoadjuvant therapy (NAT) for pancreatic ductal adenocarcinoma (PDA) are needed to optimize treatment decisions and long-term outcomes. OBJECTIVE. The purpose of this study was to investigate metrics from PET/MRI and CT to assess pathologic response of PDA to NAT and to predict overall survival (OS). METHODS. This retrospective study included 44 patients with ¹⁸F-FDG-avid borderline resectable or locally advanced PDA on pretreatment PET/MRI who also underwent post-NAT PET/MRI before surgery between August 2016 and February 2019. Carbohydrate antigen 19-9 (CA 19-9) level, metabolic metrics from PET/MRI, and morphologic metrics from CT (n = 34) were compared between pathologic responders (College of American Pathologists scores 0 and 1) and nonresponders (scores 2 and 3). AUCs were measured for metrics significantly associated with pathologic response. Relation to OS was evaluated with Cox proportional hazards models. RESULTS. Among 44 patients (22 men, 22 women; mean age, 62 ± 11.6 years), 19 (43%) were responders, and 25 (57%) were nonresponders. Median OS was 24 months (range, 6-42 months). Before treatment, responders and nonresponders did not differ in CA 19-9 level, metabolic metrics, or CT metrics (p > .05). After treatment, responders and nonresponders differed in complete metabolic response (CMR) (responders, 89% [17/19]; nonresponders, 40% [10/25]; p = .04], mean change in SUV_max (ΔSUV_max; responders, -70% ± 13%; nonresponders, -37% ± 42%; p < .001), mean change in SUV_max corrected to serum glucose level (ΔSUV_gluc) (responders, -74% ± 12%; nonresponders, -30% ± 58%; p < .001), RECIST response on CT (responders, 93% [13/14]; nonresponders, 50% [10/20]; p = .02)], and mean change in tumor volume on CT (ΔTvol) (responders, -85% ± 21%; nonresponders, 57% ± 400%; p < .001). The AUC of CMR for pathologic response was 0.75; ΔSUV_max, 0.83; ΔSUV_gluc, 0.87; RECIST, 0.71; and ΔTvol 0.86. The AUCs of bivariable PET/MRI and CT models were 0.83 (CMR and ΔSUV_max), 0.87 (CMR and ΔSUV_gluc), and 0.87 (RECIST and ΔTvol). OS was associated with CMR (p = .03), ΔSUV_max (p = .003), ΔSUV_gluc (p = .003), and RECIST (p = .046). CONCLUSION. Unlike CA 19-9 level, changes in metabolic metrics from PET/MRI and morphologic metrics from CT after NAT were associated with pathologic response and OS in patients with PDA, warranting prospective validation. CLINICAL IMPACT. Imaging metrics associated with pathologic response and OS in PDA could help guide clinical management and outcomes for patients with PDA who undergo emergency therapeutic interventions.

Pancreatic ductal adenocarcinoma: tumour regression grading following neoadjuvant FOLFIRINOX and radiation

AIMS

In the adjuvant setting, when compared to gemcitabine, patients with pancreatic ductal adenocarcinoma (PDAC) treated with FOLFIRINOX (Folinic Acid, Fluorouracil, Irinotecan, and Oxaliplatin) show superior survival. In this study, we quantitatively assess the pathological tumour response to chemoradiation in pancreatectomy specimens and reassess guidelines for tumour regression grading.

METHODS AND RESULTS

We evaluated 92 patients with borderline resectable/locally advanced PDAC following pancreatectomy and neoadjuvant treatment with FOLFIRINOX and radiation. Demographic data, CAP tumour regression grade (TRG) and overall survival (OS) were recorded. A quantitative analysis of residual tumour was performed on the slide with the highest tumour burden to derive a tumour-to-tumour bed ratio. On univariate analysis, only lymph node status (P = 0.043) and CAP TRG (P = 0.038) correlated with OS. Sixteen per cent of patients showed a complete pathological response. The optimal tumour-to-tumour bed ratio cut-point was 11.6%, and on a multivariate model was the only pathological parameter that correlated with OS (P = 0.016) (hazard ratio = 2.27).

CONCLUSIONS

The high proportion of patients with PDAC showing complete and near-complete pathological responses supports the use of FOLFIRINOX and radiation in the neoadjuvant setting. Several traditional pathology parameters fail to predict OS in patients treated with chemoradiation, while a quantitative tumour-to-tumour bed ratio is a powerful predictor of OS. The data support a two-tiered approach to TRG based on tumour-to-tumour bed ratio, and quantitative analysis merits further consideration.

Fibrotic Response to Neoadjuvant Therapy Predicts Survival in Pancreatic Cancer and Is Measurable with Collagen-Targeted Molecular MRI

PURPOSE

To evaluate the prognostic value of posttreatment fibrosis in human PDAC patients, and to compare a type I collagen targeted MRI probe, CM-101, to the standard contrast agent, Gd-DOTA, for their abilities to identify FOLFIRINOX-induced fibrosis in a murine model of PDAC.

EXPERIMENTAL DESIGN

Ninety-three chemoradiation-treated human PDAC samples were stained for fibrosis and outcomes evaluated. For imaging, C57BL/6 and FVB mice were orthotopically implanted with PDAC cells and FOLFIRINOX was administered. Mice were imaged with Gd-DOTA and CM-101.

RESULTS

In humans, post-chemoradiation PDAC tumor fibrosis was associated with longer overall survival (OS) and disease-free survival (DFS) on multivariable analysis (OS P = 0.028, DFS P = 0.047). CPA increased the prognostic accuracy of a multivariable logistic regression model comprised of previously established PDAC risk factors [AUC CPA (-) = 0.76, AUC CPA (+) = 0.82]. In multiple murine orthotopic PDAC models, FOLFIRINOX therapy reduced tumor weight (P < 0.05) and increased tumor fibrosis by collagen staining (P < 0.05). CM-101 MR signal was significantly increased in fibrotic tumor regions. CM-101 signal retention was also increased in the more fibrotic FOLFIRINOX-treated tumors compared with untreated controls (P = 0.027), consistent with selective probe binding to collagen. No treatment-related differences were observed with Gd-DOTA imaging.

CONCLUSIONS

In humans, post-chemoradiation tumor fibrosis is associated with OS and DFS. In mice, our MR findings indicate that translation of collagen molecular MRI with CM-101 to humans might provide a novel imaging technique to monitor fibrotic response to therapy to assist with prognostication and disease management.

Reduced and Normalized Carbohydrate Antigen 19-9 Concentrations after Neoadjuvant Chemotherapy Have Comparable Prognostic Performance in Patients with Borderline Resectable and Locally Advanced Pancreatic Cancer

BACKGROUND

The association between optimal carbohydrate antigen (CA) 19-9 concentration after neoadjuvant chemotherapy (NACT) and prognosis has not been confirmed in patients with borderline resectable (BRPC) and locally advanced pancreatic cancer (LAPC).

METHODS

This retrospective study included 122 patients with BRPC and 103 with LAPC who underwent surgery after NACT between 2012 and 2019 in a tertiary referral center. Prognostic models were established based on relative difference of the CA 19-9 (RDC), with their prognostic performance compared using C-index and Akaike information criterion (AIC).

RESULTS

CA 19-9 concentrations of 37-1000 U/mL before NACT showed prognostic significance in patients with BRPC and LAPC (hazard ratio [HR]: 0.262; 95% confidence interval [CI]: 0.092-0.748; p = 0.012). Prognostic models in this subgroup showed that RDC was independently prognostic of better overall survival (HR: 0.262; 95% CI: 0.093-0.739; p = 0.011) and recurrence free survival (HR: 0.299; 95% CI: 0.140-0.642; p = 0.002). The prognostic performances of RDC (C-index: 0.653; AIC: 227.243), normalization of CA 19-9 after NACT (C-index: 0.625; AIC: 230.897) and surgery (C-index: 0.613; AIC: 233.114) showed no significant differences.

CONCLUSION

RDC was independently associated with better prognosis after NACT in patients with BRPC or LAPC. Decreased CA19-9 after NACT was a prognostic indicator of better survival and recurrence, as was normalization of CA 19-9 after both NACT and surgery.

Predicting Rectal Cancer Response to Neoadjuvant Chemoradiotherapy Using Deep Learning of Diffusion Kurtosis MRI

Background Preoperative response evaluation with neoadjuvant chemoradiotherapy remains a challenge in the setting of locally advanced rectal cancer. Recently, deep learning (DL) has been widely used in tumor diagnosis and treatment and has produced exciting results. Purpose To develop and validate a DL method to predict response of rectal cancer to neoadjuvant therapy based on diffusion kurtosis and T2-weighted MRI. Materials and Methods In this prospective study, participants with locally advanced rectal adenocarcinoma (≥cT3 or N+) proved at histopathology and baseline MRI who were scheduled to undergo preoperative chemoradiotherapy were enrolled from October 2015 to December 2017 and were chronologically divided into 308 training samples and 104 test samples. DL models were constructed primarily to predict pathologic complete response (pCR) and secondarily to assess tumor regression grade (TRG) (TRG0 and TRG1 vs TRG2 and TRG3) and T downstaging. Other analysis included comparisons of diffusion kurtosis MRI parameters and subjective evaluation by radiologists. Results A total of 383 participants (mean age, 57 years ± 10 [standard deviation]; 229 men) were evaluated (290 in the training cohort, 93 in the test cohort). The area under the receiver operating characteristic curve (AUC) was 0.99 for the pCR model in the test cohort, which was higher than the AUC for raters 1 and 2 (0.66 and 0.72, respectively; P < .001 for both). AUC for the DL model was 0.70 for TRG and 0.79 for T downstaging. AUC for pCR with the DL model was better than AUC for the best-performing diffusion kurtosis MRI parameters alone (diffusion coefficient in normal diffusion after correcting the non-Gaussian effect [D_app value] before neoadjuvant therapy, AUC = 0.76). Subjective evaluation by radiologists yielded a higher error rate (1 - accuracy) (25 of 93 [26.9%] and 23 of 93 [24.8%] for raters 1 and 2, respectively) in predicting pCR than did evaluation with the DL model (two of 93 [2.2%]); the radiologists achieved a lower error rate (12 of 93 [12.9%] and 13 of 93 [14.0%] for raters 1 and 2, respectively) when assisted by the DL model. Conclusion A deep learning model based on diffusion kurtosis MRI showed good performance for predicting pathologic complete response and aided the radiologist in assessing response of locally advanced rectal cancer after neoadjuvant chemoradiotherapy. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Koh in this issue.

Tumor Regression Grading Assessment in Locally Advanced Pancreatic Cancer After Neoadjuvant FOLFIRINOX: Interobserver Agreement and Prognostic Implications

Neoadjuvant therapy represents an increasingly used strategy in pancreatic cancer, and this means that more pancreatic resections need to be evaluated for therapy effect. Several grading systems have been proposed for the histological assessment of tumor regression in pre-treated patients with pancreatic cancer, but issues like practical application, level of agreement and prognostic significance are still debated. To date, a standardized and widely accepted score has not been established yet. In this study, two pathologists with expertise in pancreatic cancer used 4 of the most frequently reported systems (College of American Pathologists, Evans, MD Anderson, and Hartman) to evaluate tumor regression in 29 locally advanced pancreatic cancers previously treated with modified FOLFIRINOX regimen, to establish the level of agreement between pathologists and to determine their potential prognostic value. Cases were additionally evaluated with a fifth grading system inspired to the Dworak score, normally used for colo-rectal cancer, to identify an alternative, relevant option. Results obtained for current grading systems showed different levels of agreement, and they often proved to be very subjective and inaccurate. In addition, no significant correlation was observed with survival. Interestingly, Dworak score showed a higher degree of concordance and a significant correlation with overall survival in individual assessments. These data reflect the need to re-evaluate grading systems for pancreatic cancer to establish a more reproducible and clinically relevant score.

Comparison of Tumor Regression Grading of Residual Pancreatic Ductal Adenocarcinoma Following Neoadjuvant Chemotherapy Without Radiation: Would Fewer Tier-Stratification Be Favorable Toward Standardization?

To assess whether the College of American Pathologists (CAP) and the Evans grading systems for neoadjuvant chemotherapy without radiation-treated pancreatectomy specimens are prognostic, and if a 3-tier stratification scheme preserves data granularity. Conducted retrospective review of 32 patients with ordinary pancreatic ductal adenocarcinoma treated with neoadjuvant therapy without radiation followed by surgical resection. Final pathologic tumor category (AJCC eighth edition) was 46.9% ypT1, 34.4% ypT2, and 18.7% ypT3. Median follow-up time was 29.8 months, median disease-free survival (DFS) was 19.6 months, and median overall survival (OS) was 34.2 months. CAP score 1, 2, 3 were present in 5 (15.6%), 18 (56.3%), and 9 (28.1%) patients, respectively. Evans grade III, IIb, IIa, and I were present in 10 (31.2%), 8 (25.0%), 7 (21.9%), and 7 (21.9%) patients, respectively. OS (CAP: P=0.005; Evans: P=0.001) and DFS (CAP: P=0.003; Evans: P=0.04) were statistically significant for both CAP and Evans. Stratified CAP scores 1 and 2 versus CAP score 3 was statistically significant for both OS (P=0.002) and DFS (P=0.002). Stratified Evans grades I, IIa, and IIb versus Evans grade III was statistically significant for both OS (P=0.04) and DFS (P=0.02). CAP, Evans, and 3-tier stratification are prognostic of OS and DFS.

Efficacy and feasibility of stereotactic radiotherapy after folfirinox in patients with locally advanced pancreatic cancer (LAPC-1 trial)

BACKGROUND

We conducted a multicentre phase II trial to investigate feasibility and antitumor activity of sequential FOLFIRINOX and Stereotactic Body Radiotherapy (SBRT) in patients with locally advanced pancreatic cancer (LAPC), (LAPC-1 trial).

METHODS

Patients with biopsy-proven LAPC treated in four hospitals in the Netherlands between December 2014 and June 2017. Patients received 8 cycles of FOLFIRINOX followed by SBRT (5 fractions/8 Gy) if no tumour progression after the FOLFIRINOX treatment was observed. Primary outcome was 1-year overall survival (OS). Secondary outcomes were median OS, 1-year progression-free survival (PFS), treatment-related toxicity, and resection rate. The study is registered with ClinicalTrials.gov, NCT02292745, and is completed.

FINDINGS

Fifty patients were included. Nineteen (38%) patients did not receive all 8 cycles of FOLFIRINOX, due to toxicity (n = 12), disease progression (n = 6), or patients' preference (n = 1). Thirty-nine (78%) patients received the SBRT treatment. The 1-year OS and PFS were 64% (95% CI: 50%-76%) and 34% (95% CI: 22%-48%), respectively. Thirty grade 3 or 4 adverse events were observed during FOLFIRINOX. Two (5%) grade 3 or 4 adverse events after SBRT were observed. Two (5%) patients died due to a gastro-intestinal bleeding within three months after SBRT were observed. Six (12%) patients underwent a resection, all resulting in a complete (R0) resection. Two patients had a complete pathological response.

INTERPRETATION

FOLFIRINOX followed by SBRT in patients with LAPC is feasible and shows relevant antitumor activity. In 6 (12%) patients a potentially curative resection could be pursued following this combined treatment, with a complete histological response being observed in two patients.

Area of residual tumor (ART) can predict prognosis after post neoadjuvant therapy resection for pancreatic ductal adenocarcinoma

An increasing number of patients with pancreatic ductal adenocarcinoma (PDAC) have undergone resection after neoadjuvant therapy (NAT). We have reported Area of Residual Tumor (ART) as a useful pathological assessment method to predict patient outcomes after post NAT resection in various cancer types. The aim of this study was to assess the prognostic performance of ART in PDAC resected after NAT. Sixty-three patients with PDAC after post NAT resection were analyzed. The viable residual tumor area was outlined and the measurement of ART was performed using morphometric software. The results were compared with those of the College of American Pathologist (CAP) regression grading. Of 63 cases, 39 (62%) patients received chemoradiation therapy and 24 (38%) received chemotherapy only. The median value of ART was 163 mm2. Large ART with 220 mm2 as the cut-off was significantly associated with lymphatic invasion, vascular invasion and perineural invasion, while CAP regression grading was not associated with any clinicopathological features. By multivariate analysis, large ART (≥220 mm2) was an independent predictor of shorter relapse free survival. Together with our previous reports, an ART-based pathological assessment may become a useful method to predict patient outcomes after post NAT resection across various cancer types.

Pathology assessment of pancreatic cancer following neoadjuvant treatment: Time to move on

Neoadjuvant treatment has increasingly become an integral part of the multimodal management of patients with pancreatic cancer. In patients who are able to undergo surgery following preoperative therapy, tumour regression grading remains the diagnostic gold standard for the histomorphological assessment of the effect of neoadjuvant treatment. In recent years, however, there has been growing concern about inherent flaws of tumour regression grading systems as well as their imprecise and impractical criteria that result in divergence of practice and lack of interobserver agreement. Furthermore, existing tumour regression systems differ in their defining criteria and thresholds, leading to incomparability of data. In this review, the principles and limitations of the main existing tumour regression systems are discussed, and potential alternative assessment approaches and novel markers are presented.