Histopathological diagnosis of tumour deposits in colorectal cancer: a Delphi consensus study

An internally and externally validated nomogram for predicting cancer-specific survival in octogenarians after radical resection for colorectal cancer

AIMS

We aimed to develop an elaborative nomogram that predicts cancer-specific survival (CSS) in American and Chinese octogenarians treated with radical resection for CRC.

METHODS

The patient data of newly diagnosed patients aged 80 years or older who underwent radical resection for CRC from 2010 to 2015 were extracted from the Surveillance, Epidemiology, and End Results (SEER) database and then randomly divided into a training cohort and a validation cohort. The patients collected from our hospital were defined as the external validation cohort. Univariate and multivariate Cox regression was used to select independent predictive factors for the construction of a nomogram to predict 1-, 2- and 3-year CSS.

RESULTS

The multivariate Cox regression model identified age, T stage, N stage, perineural invasion, chemotherapy, tumour deposits, carcinoembryonic antigen level, number of lymph node metastases, and number of solid organ metastases as independent predictors of survival. The C-index of the nomogram for 1-, 2- and 3-year CSS was 0.758, 0.762, and 0.727, respectively, demonstrating significant clinical value and substantial reliability compared to the TNM stage. The calibration curve and area under the curve also indicated considerable predictive accuracy. In addition, decision curve analysis demonstrated desirable net benefits in clinical application.

CONCLUSION

We constructed a nomogram for predicting the CSS of individual octogenarian patients with CRC who underwent radical resection. The nomogram performed better than the TNM staging system in this particular population and could guide clinicians in clinical follow-up and individual therapeutic plan formulation.

Evaluating the prognostic value of tumor deposits in non-metastatic lymph node-positive colon adenocarcinoma using Cox regression and machine learning

BACKGROUND

The 8th AJCC TNM staging for non-metastatic lymph node-positive colon adenocarcinoma patients(NMLP-CA) stages solely by lymph node status, irrespective of the positivity of tumor deposits (TD). This study uses machine learning and Cox regression to predict the prognostic value of tumor deposits in NMLP-CA.

METHODS

Patient data from the SEER registry (2010-2019) was used to develop CSS nomograms based on prognostic factors identified via multivariate Cox regression. Model performance was evaluated by c-index, dynamic calibration, and Schmid score. Shapley additive explanations (SHAP) were used to explain the selected models.

RESULTS

The study included 16,548 NMLP-CA patients, randomized 7:3 into training (n = 11,584) and test (n = 4964) sets. Multivariate Cox analysis identified TD, age, marital status, primary site, grade, pT stage, and pN stage as prognostic for cancer-specific survival (CSS). In the test set, the gradient boosting machine (GBM) model achieved the best C-index (0.733) for CSS prediction, while the Cox model and GAMBoost model optimized dynamic calibration(6.473) and Schmid score (0.285), respectively. TD ranked among the top 3 most important features in the models, with increasing predictive significance over time.

CONCLUSIONS

Positive tumor deposit status confers worse prognosis in NMLP-CA patients. Tumor deposits may confer higher TNM staging. Furthermore, TD could play a more significant role in the staging system.

Multimodality Imaging to Direct Management of Primary and Recurrent Rectal Adenocarcinoma Beyond the Total Mesorectal Excision Plane

Rectal tumors extending beyond the total mesorectal excision (TME) plane (beyond-TME) require particular multidisciplinary expertise and oncologic considerations when planning treatment. Imaging is used at all stages of the pathway, such as local tumor staging/restaging, creating an imaging-based "roadmap" to plan surgery for optimal tumor clearance, identifying treatment-related complications, which may be suitable for radiology-guided intervention, and to detect recurrent or metastatic disease, which may be suitable for radiology-guided ablative therapies. Beyond-TME and exenterative surgery have gained acceptance as potentially curative procedures for advanced tumors. Understanding the role, techniques, and pitfalls of current imaging techniques is important for both radiologists involved in the treatment of these patients and general radiologists who may encounter patients undergoing surveillance or patients presenting with surgical complications or intercurrent abdominal pathology. This review aims to outline the current and emerging roles of imaging in patients with beyond-TME and recurrent rectal malignancy, focusing on practical tips for image interpretation and surgical planning in the beyond-TME setting. Keywords: Abdomen/GI, Rectum, Oncology © RSNA, 2024.

Tumor deposits in axillary adipose tissue in patients with breast cancer: Do they matter?

Tumor deposits (TDs) are defined as discrete, irregular clusters of tumor cells lying in the soft tissue adjacent to but separate from the primary tumor, and are usually found in the lymphatic drainage area of the primary tumor. By definition, no residual lymph node structure should be identified in these tumor masses. At present, TDs are mainly reported in colorectal cancer, with a few reports in gastric cancer. There are very few reports on breast cancer (BC). For TDs, current dominant theories suggest that these are the result of lymph node metastasis of the tumor with complete destruction of the lymph nodes by the tumor tissue. Even some pathologists classify a TD as two lymph node metastases for calculation. Some pathologists also believe that TDs belong to the category of disseminated metastasis. Therefore, regardless of the origin, TDs are an indicator of poor prognosis. Moreover, for BC, sentinel lymph node biopsy is generally used at present. Whether radical axillary lymph node dissection should be adopted for BC with TDs in axillary lymph nodes is still inconclusive. The present commentary of this clinical issue has certain guiding significance. It is aimed to increase the awareness of the scientific community towards this under-recognized problem in BC pathology.

Isolated axillary tumor deposit consistent with primary breast carcinoma: A case report

BACKGROUND

We all know that lymph-node metastasis is an important factor for poor clinical outcome in breast cancer prognosis. Tumor deposit refers to a discrete collection of cancer cells that is found in the lymph nodes or other tissues adjacent to the primary tumor site. These tumor deposits are separate from the primary tumor and are often considered as a manifestation of lymph node metastasis. In gastric and colorectal cancer, tumor deposits in the lymph node drainage area have been included as independent prognostic factors. The question arises whether tumor deposits should also be considered as prognostic factors in breast cancer patients. This article aims to provoke some thoughts on this matter through a case study and literature review.

CASE SUMMARY

A 70-year-old female patient was found to have a right breast lump for over 2 years. On January 3, 2023, a core needle biopsy of the right breast lump was performed, and the pathology report indicated invasive carcinoma. Subsequently, on January 17, 2023, the patient underwent right breast-conserving surgery, sentinel lymph node biopsy, and right axillary lymph node dissection. The postoperative pathological staging was determined as stage IIB. The patient received chemotherapy, radiotherapy, and endocrine therapy. At present, nearly one year after the surgery, no obvious signs of metastasis have been observed in the follow-up examinations, but the long-term prognosis is still unknown.

CONCLUSION

There is a need for increased focus on the matter of tumor deposits in the lymph node drainage region, as well as a requirement for further clinical investigation to ascertain the relevance of tumor deposits in the prognosis of individuals with breast carcinoma.

Tumour deposits in colon cancer predict recurrence and reduced survival in a nationwide population-based study

BACKGROUND

Tumour deposits are suggested to impact prognosis in colon cancer negatively. This study assessed the impact of tumour deposits on oncological outcomes.

METHODS

Data from the Swedish Colorectal Cancer Registry for patients who underwent R0 abdominal surgery for TNM stage I-III colon cancer between 2011 and 2014 with 5-year follow-up were analysed with multivariable analysis. Patients were categorized for their tumour deposit status and compared for the local recurrence and distant metastasis rates and 5-year survivals (overall and relative). Subgroup analyses were performed according to the nodal disease status.

RESULTS

Of 8146 stage I-III colon cancer patients who underwent R0 resection, 8014 patients were analysed (808 tumour deposits positive, 7206 tumour deposits negative). Patients with tumour deposits positive tumours had increased local recurrence and distant metastasis rates (7.2 versus 3.0 per cent; P < 0.001 and 33.9 versus 12.0 per cent; P < 0.001 respectively) and reduced 5-year overall and relative survival (56.8 per cent versus 74.9 per cent; P < 0.001 and 68.5 versus 92.6 per cent; P < 0.001 respectively). In multivariable analysis, tumour deposits moderately increased the risks of local recurrence and distant metastasis (hazard ratio 1.50, 95 per cent c.i. 1.09 to 2.07; P = 0.013 and HR 1.91, 95 per cent c.i. 1.64 to 2.23; P < 0.001 respectively) and worse 5-year overall and relative survival (hazard ratio 1.60, 95 per cent c.i. 1.40 to 1.82; P < 0.001 and excess hazard ratio 2.24, 95 per cent c.i. 1.81 to 2.78; P < 0.001 respectively). Subgroup analysis of N stages found that N1c patients had worse outcomes than N0 for distant metastasis and relative survival. For patients with lymph node metastases tumour deposits increased the risks of distant metastasis and worse overall and relative survival, except for N2b patients.

CONCLUSION

Tumour deposits negatively impact the prognosis in colon cancer and must be considered when discussing adjuvant chemotherapy.

A novel risk model for predicting peritoneal metastasis in colorectal cancer based on the SEER database

BACKGROUND

Early detection and intervention could significantly improve the prognosis of patients with peritoneal metastasis (PM). Our main purpose was to develop a model to predict the risk of PM in patients with colorectal cancer (CRC).

METHODS

Patients from the Surveillance, Epidemiology, and End Results (SEER) database with CRC classified according to the AJCC 8th TNM staging system were selected for the study. After data pre-processing, the dataset was divided into a training set and a validation set. In the training set, univariate logistic analysis and stepwise multivariate logistic regression analysis were utilized to screen clinical features and construct a risk prediction model. Then, we validated the model using the confusion matrix, receiver operating characteristic (ROC) curves, decision curve analysis (DCA), and calibration curves to examine its performance.

RESULTS

The model constructed using stepwise multivariate logistic regression analysis incorporated the following eight clinical features: age, tumor location, histological type, T stage, carcinoembryonic antigen (CEA) level, tumor deposits (TDs), log odds (LODDS) of metastatic lymph nodes, and extraperitoneal metastasis (EM). The areas under the curve (AUCs) of the model in the training and validation sets were 0.924 and 0.912, respectively. The accuracy and the recall ratio were higher than 0.8 in both cohorts. DCA and the calibration curves also confirmed its excellent predictive power.

CONCLUSIONS

Our model can effectively predict the risk of PM in CRC patients, which is of great significance for the timely identification of patients at high risk of PM and further clinical decision-making.

Development and validation of a nomogram for preoperative prediction of tumor deposits in colorectal cancer

BACKGROUND

Based on the clinical data of colorectal cancer (CRC) patients who underwent surgery at our institution, a model for predicting the formation of tumor deposits (TDs) in this patient population was established.

AIM

To establish an effective model for predicting TD formation, thus enabling clinicians to identify CRC patients at high risk for TDs and implement personalized treatment strategies.

METHODS

CRC patients (n = 645) who met the inclusion criteria were randomly divided into training (n = 452) and validation (n = 193) cohorts using a 7:3 ratio in this retrospective analysis. Least absolute shrinkage and selection operator regression was employed to screen potential risk factors, and multivariable logistic regression analysis was used to identify independent risk factors. Subsequently, a predictive model for TD formation in CRC patients was constructed based on the independent risk factors. The discrimination ability of the model, its consistency with actual results, and its clinical applicability were evaluated using receiver-operating characteristic curves, area under the curve (AUC), calibration curves, and decision curve analysis (DCA).

RESULTS

Thirty-four (7.5%) patients with TDs were identified in the training cohort based on postoperative pathological specimens. Multivariate logistic regression analysis identified female sex, preoperative intestinal obstruction, left-sided CRC, and lymph node metastasis as independent risk factors for TD formation. The AUCs of the nomogram models constructed using these variables were 0.839 and 0.853 in the training and validation cohorts, respectively. The calibration curve demonstrated good consistency, and the training cohort DCA yielded a threshold probability of 7%-78%.

CONCLUSION

This study developed and validated a nomogram with good predictive performance for identifying TDs in CRC patients. Our predictive model can assist surgeons in making optimal treatment decisions.

Clinical significance of metastatic tumor deposit foci in rectal cancer in the lateral pelvic lymph node area

BACKGROUND

Although previous studies have demonstrated that tumor deposits (TDs) are associated with worse prognosis in colon cancer, their clinical significance in rectal cancer has not been fully elucidated, especially in the lateral pelvic lymph node (LPLN) area. This study aimed to clarify the clinical significance of TDs, focusing on the number of metastatic foci, including lymph node metastases (LNMs) and TDs, in the LPLN area.

METHODS

This retrospective study involved 226 consecutive patients with cStage II/III low rectal cancer who underwent LPLN dissection. Metastatic foci, including LNM and TD, in the LPLN area were defined as lateral pelvic metastases (LP-M) and were evaluated according to LP-M status: presence (absence vs. presence), histopathological classification (LNM vs. TD), and number (one to three vs. four or more). We evaluated the relapse-free survival of each model and compared them using the Akaike information criterion (AIC) and Harrell's concordance index (c-index).

RESULTS

Forty-nine of 226 patients (22%) had LP-M, and 15 patients (7%) had TDs. The median number of LP-M per patient was one (range, 1-9). The best risk stratification power was observed for number (AIC, 758; c-index, 0.668) compared with presence (AIC, 759; c-index, 0.665) and histopathological classification (AIC, 761; c-index, 0.664). The number of LP-M was an independent prognostic factor for both relapse-free and overall survival, and was significantly associated with cumulative local recurrence.

CONCLUSION

The number of metastatic foci, including LNMs and TDs, in the LPLN area is useful for risk stratification of patients with low rectal cancer.

Alterations in Natural Killer Cells in Colorectal Cancer Patients with Stroma AReactive Invasion Front Areas (SARIFA)

BACKGROUND

Recently, our group introduced Stroma AReactive Invasion Front Areas (SARIFA) as an independent prognostic predictor for a poorer outcome in colon cancer patients, which is probably based on immunologic alterations combined with a direct tumor-adipocyte interaction: the two together reflecting a distinct tumor biology. Considering it is already known that peripheral immune cells are altered in colorectal cancer (CRC) patients, this study aims to investigate the changes in lymphocyte subsets in SARIFA-positive cases and correlate these changes with the local immune response.

METHODS

Flow cytometry was performed to analyze B, T, and natural killer (NK) cells in the peripheral blood (PB) of 45 CRC patients. Consecutively, lymphocytes in PB, tumor-infiltrating lymphocytes (TILs), and CD56+ and CD57+ lymphocytes at the invasion front and the tumor center were compared between patients with SARIFA-positive and SARIFA-negative CRCs.

RESULTS

Whereas no differences could be observed regarding most PB lymphocyte populations as well as TILs, NK cells were dramatically reduced in the PB of SARIFA-positive cases. Moreover, CD56 and CD57 immunohistochemistry suggested SARIFA-status-dependent changes regarding NK cells and NK-like lymphocytes in the tumor microenvironment.

CONCLUSION

This study proves that our newly introduced biomarker, SARIFA, comes along with distinct immunologic alterations, especially regarding NK cells.

Prognostic impact of tumor deposits on overall survival in colorectal cancer: Based on Surveillance, Epidemiology, and End Results database

BACKGROUND

In colorectal cancer, tumor deposits (TDs) are considered to be a prognostic factor in the current staging system, and are only considered in the absence of lymph node metastases (LNMs). However, this definition and the subsequent prognostic value based on it is controversial, with various hypotheses. TDs may play an independent role when it comes to survival and addition of TDs to LNM count may predict the prognosis of patients more accurately.

AIM

To assess the prognostic impact of TDs and evaluate the effect of their addition to the LNM count.

METHODS

The patients are derived from the Surveillance, Epidemiology, and End Results database. A prognostic analysis regarding impact of TDs on overall survival (OS) was performed using Cox regression model, and other covariates associating with OS were adjusted. The effect of addition of TDs to LNM count on N restaging was also evaluated. The subgroup analysis was performed to explore the different profile of risk factors between patients with and without TDs.

RESULTS

Overall, 103755 patients were enrolled with 14131 (13.6%) TD-positive and 89624 (86.4%) TD-negative tumors. TD-positive patients had worse prognosis compared with TD-negative patients, with 3-year OS rates of 47.3% (95%CI, 46.5%-48.1%) and 77.5% (95%CI, 77.2%-77.8%, P < 0.0001), respectively. On multivariable analysis, TDs were associated poorer OS (hazard ratio, 1.35; 95%CI, 1.31-1.38; P < 0.0001). Among TD-positive patients, the number of TDs had a linear negative effect on disease-free survival and OS. After reclassifying patients by adding TDs to the LNM count, 885 of 19 965 (4.4%) N1 patients were restaged as pN2, with worse outcomes than patients restaged as pN1 (3-year OS rate: 78.5%, 95%CI, 77.9%-79.1% vs 63.2%, 95%CI, 60.1%-66.5%, respectively; P < 0.0001).

CONCLUSION

TDs are an independent prognostic factor for OS in colorectal cancer. The addition of TDs to LNM count improved the prognostic accuracy of tumor, node and metastasis staging.

The new 'coN' staging system combining lymph node metastasis and tumour deposit provides a more accurate prognosis for TNM stage III colon cancer

OBJECTIVE

Despite controversy over its origin and definition, the significance of tumour deposit (TD) has been underestimated in the tumour node metastasis (TNM) staging system for colon cancer, especially in stage III patients. We aimed to further confirm the prognostic value of TD in stage III colon cancer and to establish a more accurate 'coN' staging system combining TD and lymph node metastasis (LNM).

METHODS

Information on stage III colon cancer patients with a definite TD status was retrospectively collected from the Surveillance, Epidemiology and End Results (SEER) database between 2010 and 2017. The effect of TD on prognosis was estimated using Cox regression analysis. Maximally selected rank statistics were used to select the optimal cut-off value of TD counts. The predictive power of conventional N staging and the new coN staging was evaluated and compared by Akaike's information criterion (AIC), Harrell's concordance index (C-index) and time-dependent receiver operating characteristic (ROC) curves. Clinicopathological data of stage III colon cancer patients in the Xiangya database from 2014 to 2018 were collected to validate the coN staging system.

RESULTS

A total of 39,185 patients with stage III colon cancer were included in our study: 38,446 in the SEER cohort and 739 in the Xiangya cohort. The incidence of TD in stage III colon cancer was approximately 30% (26% in SEER and 30% in the Xiangya database). TD was significantly associated with poorer overall survival (OS) (HR = 1.37, 95% CI 1.31-1.44, p < 0.001 in SEER). The optimal cut-off value of TD counts was 4, and the patients were classified into the TD0 (count = 0), TD1 (count = 1-3) and TD2 (count ≥ 4) groups accordingly. The estimated 5-year OS was significantly different among the three groups (69.4%, 95% CI 68.8%-70.0% in TD0; 60.5%, 95% CI 58.9%-62.2% in TD1 and 42.6%, 95% CI 39.2%-46.4% in TD2, respectively, p < 0.001). The coN system integrating LNM and TD was established, and patients with stage III colon cancer were reclassified into five subgroups (coN1a, coN1b, coN2a, coN2b and coN2c). Compared with conventional N staging, the coN staging Cox model had a smaller AIC (197097.581 vs. 197358.006) and a larger C-index (0.611 vs. 0.601). The AUCs of coN staging at 3, 5 and 7 years were also greater than those of conventional N staging (0.6305, 0.6326, 0.6314 vs. 0.6186, 0.6197, 0.6160). Concomitant with the SEER cohort results, the coN staging Cox model of the Xiangya cohort also had a smaller AIC (2883.856 vs. 2906.741) and a larger C-index (0.669 vs. 0.633). Greater AUCs at 3, 5 and 7 years for coN staging were also observed in the Xiangya cohort (0.6983, 0.6774, 0.6502 vs. 0.6512, 0.6368, 0.6199).

CONCLUSIONS

Not only the presence but also the number of TDs is associated with poor prognosis in stage III colon cancer. A combined N staging system integrating LNM and TD provides more accurate prognostic prediction than the latest AJCC N staging in stage III colon cancer.

Developing consensus in Histopathology: the role of the Delphi method

The Delphi method is a well-established research tool, used for consensus building across a number of fields. Despite its widespread use, and popularity in many medical specialities, there is a paucity of literature on the use of the Delphi method in Histopathology. This literature review seeks to critique the Delphi methodology and explore its potential applications to histopathology-based clinical and research questions. We review those published studies that have utilized the Delphi methodology in Histopathology settings and specifically outline the advantages and limitations of this technique, highlighting situations where its application can be most effective.

Lymph Nodes Evaluation in Rectal Cancer: Where Do We Stand and Future Perspective

The assessment of nodal involvement in patients with rectal cancer (RC) is fundamental in disease management. Magnetic Resonance Imaging (MRI) is routinely used for local and nodal staging of RC by using morphological criteria. The actual dimensional and morphological criteria for nodal assessment present several limitations in terms of sensitivity and specificity. For these reasons, several different techniques, such as Diffusion Weighted Imaging (DWI), Intravoxel Incoherent Motion (IVIM), Diffusion Kurtosis Imaging (DKI), and Dynamic Contrast Enhancement (DCE) in MRI have been introduced but still not fully validated. Positron Emission Tomography (PET)/CT plays a pivotal role in the assessment of LNs; more recently PET/MRI has been introduced. The advantages and limitations of these imaging modalities will be provided in this narrative review. The second part of the review includes experimental techniques, such as iron-oxide particles (SPIO), and dual-energy CT (DECT). Radiomics analysis is an active field of research, and the evidence about LNs in RC will be discussed. The review also discusses the different recommendations between the European and North American guidelines for the evaluation of LNs in RC, from anatomical considerations to structured reporting.

Current controversies in TNM for the radiological staging of rectal cancer and how to deal with them: results of a global online survey and multidisciplinary expert consensus

Objectives

To identify the main problem areas in the applicability of the current TNM staging system (8th ed.) for the radiological staging and reporting of rectal cancer and provide practice recommendations on how to handle them.

Methods

A global case-based online survey was conducted including 41 image-based rectal cancer cases focusing on various items included in the TNM system. Cases reaching < 80% agreement among survey respondents were identified as problem areas and discussed among an international expert panel, including 5 radiologists, 6 colorectal surgeons, 4 radiation oncologists, and 3 pathologists.

Results

Three hundred twenty-one respondents (from 32 countries) completed the survey. Sixteen problem areas were identified, related to cT staging in low-rectal cancers, definitions for cT4b and cM1a disease, definitions for mesorectal fascia (MRF) involvement, evaluation of lymph nodes versus tumor deposits, and staging of lateral lymph nodes. The expert panel recommended strategies on how to handle these, including advice on cT-stage categorization in case of involvement of different layers of the anal canal, specifications on which structures to include in the definition of cT4b disease, how to define MRF involvement by the primary tumor and other tumor-bearing structures, how to differentiate and report lymph nodes and tumor deposits on MRI, and how to anatomically localize and stage lateral lymph nodes.

Conclusions

The recommendations derived from this global survey and expert panel discussion may serve as a practice guide and support tool for radiologists (and other clinicians) involved in the staging of rectal cancer and may contribute to improved consistency in radiological staging and reporting.

Key Points

• Via a case-based online survey (incl. 321 respondents from 32 countries), we identified 16 problem areas related to the applicability of the TNM staging system for the radiological staging and reporting of rectal cancer.

• A multidisciplinary panel of experts recommended strategies on how to handle these problem areas, including advice on cT-stage categorization in case of involvement of different layers of the anal canal, specifications on which structures to include in the definition of cT4b disease, how to define mesorectal fascia involvement by the primary tumor and other tumor-bearing structures, how to differentiate and report lymph nodes and tumor deposits on MRI, and how to anatomically localize and stage lateral lymph nodes.

• These recommendations may serve as a practice guide and support tool for radiologists (and other clinicians) involved in the staging of rectal cancer and may contribute to improved consistency in radiological staging and reporting.

[Tumour deposition (TD), a probably underestimated poor prognostic criterion, to be taken into account in the therapeutic management of patients with stage III colon cancer]

The management of colorectal cancer (CRC) relies heavily on TNM staging. In order to improve this staging, it is essential to identify all histological markers bearing a significant prognostic value. Among these, tumor deposits (TDs), defined as tumor foci in the pericolonic or perirectal adipose tissue with no residual lymph node tissue, have been shown to be associated with poor prognosis in cohort studies leading to their individualization in the TNM7 classification as pN1c. However, TDs are only considered in the absence of lymph node metastases. There is no consensus on this particular way of integrating TDs in the TNM classification. Indeed, at the time when the choice of the type of adjuvant treatment and its duration in stage III colon cancers (i.e. with lymph node metastases) is based on pT and pN criteria, taking into account TDs only in the absence of concomitant lymph node metastases is potentially responsible for a misclassification of some patients and wrong therapeutic decisions. In addition, many questions concerning the true definition of TDs, their origin, their prognostic value and the optimization of their consideration remain open. The objective of this review is to provide a synthesis of current knowledge on TDs in CRC, in view of their prognostic importance, their biological complexity and the scientific interest they are currently the subject of.