|Year : 2019 | Volume
| Issue : 3 | Page : 449-454
A comprehensive review of surgical margin in oral squamous cell carcinoma highlighting the significance of tumor-free surgical margins
Mamata Kamat1, Bhagawan Das Rai2, Rudrayya S Puranik3, Uma Vasant Datar4
1 PhD Scholar, Faculty of Dental Sciences, Pacific Academy of Higher Education and Research University, Udaipur, Rajasthan, India
2 Department of Oral and Maxillofacial Surgery, Pacific Dental College and Hospital, Udaipur, Rajasthan, India
3 Department of Oral Pathology and Microbiology, P.M.N.M. Dental College and Hospital, Bagalkot, Karnataka, India
4 Department of Oral Pathology and Microbiology, Bharati Vidyapeeth (Deemed to be University) Dental College and Hospital, Sangli, Maharashtra, India
|Date of Web Publication||29-May-2019|
Dr. Mamata Kamat
QRTS No 7, B Block, Bharati Vidyapeeth Medical Campus, Miraj Road, Wanlesswadi, Sangli - 416 416, Maharashtra
Source of Support: None, Conflict of Interest: None
Oral squamous cell carcinoma (OSCC) is the most common malignancy of the oral cavity, and surgery is the most accepted line of treatment. The surgical margins (SMs) or resection margins are boundaries of resection specimen excised by the surgeon. The status of these resected SMs is an important and valuable tool to predict the treatment outcome. It is necessary to attain optimal SM to avoid local recurrence and improve overall survival. However, the controversies exist regarding the concept of optimal SM. There are various factors that influence the assessment of the SMs. In addition, apart from routine histopathology, the molecular assessment of resected margins has recently gained value which has a promising role for margin surveillance. Furthermore, the histological and molecular appraisal of tumor-free margins is also necessary to standardize the treatment modalities. Hence, this review aims to summarize the above issues that influence the evaluation of SMs of OSCC along with recent updates. Furthermore, an attempt has been made to give an overview about future possible approaches for the tumor-free margins. An electronic search was performed for items related to the evaluation of SMs in OSCC, and the obtained articles were critically assessed and the relevant information was extracted and summarized.
Keywords: Oral squamous cell carcinoma, surgical margins, tumor-free margins
|How to cite this article:|
Kamat M, Rai BD, Puranik RS, Datar UV. A comprehensive review of surgical margin in oral squamous cell carcinoma highlighting the significance of tumor-free surgical margins. J Can Res Ther 2019;15:449-54
|How to cite this URL:|
Kamat M, Rai BD, Puranik RS, Datar UV. A comprehensive review of surgical margin in oral squamous cell carcinoma highlighting the significance of tumor-free surgical margins. J Can Res Ther [serial online] 2019 [cited 2020 Jul 15];15:449-54. Available from: http://www.cancerjournal.net/text.asp?2019/15/3/449/241645
| > Introduction|| |
Oral squamous cell carcinoma (OSCC) is the sixth to eight most common cancer around the world. Surgical resection is the primary mode of management of OSCC followed by adjuvant radiotherapy and chemotherapy when needed. In spite of advances in diagnostic and treatment modalities, the 5-year survival rates are low at <50%., The low survival rate is attributable to locoregional recurrence and lymph node metastasis. The evidence of tumor in or close to surgical margin (SM) indicates likelihood of local relapse after resection., Hence, histological evaluation of SM is of prognostic significance. However, tumors with histologically negative margins (HNMs) are also known to demonstrate locoregional recurrence, which mandates the molecular analysis of SM to identify the residual cancer cells and to recognize genetically altered fields. Herein, we present an overview of the current approaches of SM evaluation in OSCC and emphasize the call for inclusion of “molecular status” of tumor-free margins.
Literature search of the PubMed/Medline database was performed using the following keywords or search terms: Oral, squamous cell carcinoma, surgical margins, negative resection margins, recurrence, and prognosis. Citation pearl growing technique was employed, and reference articles of the selected article were referred. After exclusion of the unrelated topics, articles in other than English language, and case reports, 38 full-text articles (including narrative reviews, n = 09; systematic reviews, n = 03; and original studies, n = 26) were included in this review.
| > Discussion|| |
Types of tumor margin
Broadly, the margins of tumor have been categorized as:
- Clinical margins: They are margins of tumor on clinical observation and palpation, which are included during resection of tumor tissue 
- SMs: SM/resection margin refers to any tissue plane where the surgeon's knife meets the patient. Along with the surface mucosa (at the edge of the tumor), it also include the submucosal and deeper connective tissues all around tumor. SMs reflect the surgeons endeavor to excise all the tumor tissue along with preservation of adjacent unaffected tissue, thus balancing the oncological and functional goals. Microscopically, SM can be further categorized into histological and molecular margins.
- Histological margins: The pathologists screen the edges/margins of resection specimen for evidence of tumor cells. The UK Royal College of Pathologists' guidelines for screening of margins propose that both the “mucosal” and “deep” (deep margins include submucosa, skeletal muscle, and bone) margins should be evaluated. According to approximation of tumor cells, mucosal and deep margins are subdivided into clear, close, and involved ,,
- Clear/negative margin: Histological distance of >5 mm from the invasive carcinoma to SMs
- Close margin: Histological distance of 1–5 mm from the invasive carcinoma to SMs
- Involved/positive margin: Histological distance of <1 mm from the invasive carcinoma to SMs. On the basis of the following histological criteria, Looser et al., suggested a classification of positive margins as: (1) margin closeness (tumor within 0.5 mm), (2) premalignant change in margin, (3) in situ cancer in margin, and (4) invasive microscopic cancer in the margin.,
Molecular margins: The histologically normal margins may harbor genetic changes. Thus, various molecular markers have been recently employed to detect these fields of genetically altered cells.,,
Assessment of surgical margins
Evaluation of resection margins is an important part of pathological examination. The status of SMs (clean/close/positive) has therapeutic and prognostic implications. Different methods have been devised for accurate assessment of SMs and subsequently the adequacy of excision of tumor. Ravi and Annavajjula  proposed a working classification of methods for evaluation of SM according to time of usage with respect to period of surgery [Table 1]. It is recommended that from the array of available methods, suitable techniques should be employed by the surgeon and/or pathologists to ensure clearance of tumor [Figure 1].
Inking of surgical margins
Accurate anatomical orientation of excised OSCC specimen and identification of all SMs forms an integral part of histopathological evaluation. The methods used for identifying SM before and after processing include use of dye/pigments, sectioning techniques, applying clips, or sutures with former being the most reliable. Due to its ease of application and clear demarcation of the borders, recently, inking of margins is commonly used. Conventionally, India ink has been used to mark the surgical resected margins. India ink is a protein based and hence it securely fixed to the tissue by cross-linked fixatives. However, the dye is more prone to wash off. Hence, multicolor inking is increasingly used (1) to examine multiple surfaces/margins, (2) for postoperative comparison of tissue planes, (3) for the benefit of postgrossing three-dimensional reconstruction, and (4) to reduce identification error when multiple sampling is required from the same tissue or when obtaining similar specimens from different patients.
Although the benefit of colored inks in surgical and histopathological practice is appreciable, the availability of these colored inks is limited. Hence, the acrylic colors have been employed as a substitute for multicolored surgical ink., It has been suggested that acrylic colors are more suitable as surgical ink than India ink because of its availability in different colors, ease of application, faster drying time, no contamination of processing fluids, easy availability, and excellent visibility in paraffin blocks and under microscope.,
Factors affecting the assessment of surgical margins
It is often observed that discrepancy exists between the SMs measured by the surgeon (which seems appropriate before/at the time of surgery) and the margins analyzed by pathologists after resection. Various factors have been postulated for this inconsistency which include
- Tissue shrinkage after resection and pathologic processing ,,
- Decrease in the dimension of the tissue under tension on surgical release from the surrounding tissue.
Tissue shrinkage is one of the important factors which cause discrepancy in the measurement of preoperative and postoperative margins. This tissue shrinkage is dependent on various intrinsic and extrinsic factors. Intrinsic factors are difference in tissue composition, tumor site, tumor stage, cohesiveness of tumor cells, degree of keratinization, degree of inflammation, and tumor site. It is also observed that shrinkage varies between different margins of a single specimen from the same location., Due to replacement of muscle by tumor tissue, intratumoral shrinkage is reported to be less compared to the shrinkage at SMs., Tissue fixation and tissue processing represent the extrinsic factors. It has been suggested that the duration of fixation does not affect the shrinkage rate of SMs. Till date, only three studies ,, have analyzed the degree of shrinkage based on anatomical location of the tumor and their findings are depicted in [Table 2]. Higher rate of tissue shrinkage is reported for margins which do not have bony support. In the light of above-mentioned findings, shrinkage should be calculated separately for each margin. Sarode and Sarode  designed a new formula for shrinkage calculation:
|Table 2: Degree of shrinkage of surgical margins obtained from different anatomical sites|
Click here to view
Where A is the microscopic distance in μm calculated with the help of image analyzer/oculometer and B is the number of basal cells within distance “A.”
Mistry et al. reported that the mean shrinkage in T1/T2 tumors is to be significantly more than that in T3/T4. This has been attributed to tumor-related destruction of contractile elements surrounding cancer. In contrast, Cheng et al. observed higher discrepancy in T3/T4 tumors than T1/T2 which has been correlated with greater microscopic invasiveness in late tumors. Both the studies differed in the anatomical sites of tumor and the number of cases studies was also limited. Hence, further studies are required to obtain a more realistic conclusion regarding SM shrinkage and tumor stage.
The mucosal elasticity is thought to influence the tumor dimension and SMs in case of buccal carcinoma. Recently, Tsai et al., in their study, found a 32.35% magnification of buccal mucosa elasticity due to stretching during maximum mouth opening and thus suggested that this elasticity should be taken into account while computing adequate SMs for transoral resection of buccal mucosa.
Optimal resection margin
Optimal SM forms a pivotal role to ensure local control and to decide adjuvant radiotherapy. The adequacy of resection depends on tumor site, anatomical restrictions, biological characteristics, and extent of surgery.,
Factors associated with rate of involved margins according to various anatomical sites are depicted in [Table 3]. Literature shows that involved mucosal margins are rare compared to involved deep margins. The pattern of tumor invasion is also suggested to influence the adequacy of margin resection. It is implicated that in tumors that invade deeply as nests and cords of cells require a wider margin than tumors with broad and flat-pushing invasive front.
In view of the above-mentioned facts, currently, “1-cm three-dimensional margin” that reflects into >5 mm of pathological margin is highly recommended. Hence, to obtain overall margin >5 mm, clinical margin for resection should be >1 cm for mucosal and deep margins and 1 cm for bony margins.
The notion of close margin is a less understood entity and there is a lack of standard definition in the head and neck region. As the lymphatic drainage, vascularization, and the presence of biologic barriers (cartilage, bone, and fascia) vary among different sites of the oral cavity, the unique definition of “close” for every site may not be practically applicable. Hence, the traditional definition of 5 mm as close needs to be re-evaluated.
While deciding the optimal SM, one should take into account the various aforementioned parameters and individualized accordingly to the patient. Furthermore, the preferred optimal SM should assist in achieving adequate local control and avoid inadequate resection or unnecessary functional morbidity from too much resection.
Histologically tumor-free surgical margins
As the entire oral mucosa is exposed to carcinogens, changes occur at histological and molecular level even at the clinically normal margins of tumor. On routine histopathology, tumor-free margins may show signs of chronic mucosal irritation, cellular atypia, and mild epithelial dysplasia and thus reported as HNMs.
Literature reports that about 10%–30% of OSCC patients with HNMs report local recurrence. The suggested reasons include (a) residual cancer cells undetected by routine histopathology (minimal residual cancer) and (b) nonresected “field of genetically altered cells” that remain macroscopically undetectable. These fields serve as fertile grounds for the evolution of potentially malignant lesions as well as invasive cancer., Majority of these altered fields can only be identified by means of immunohistochemistry (IHC) or genetic analysis.
Determining the “molecular status” of the SMs is one of the newer diagnostic methods employed in OSCC. As the genetic alterations pave the way for the phenotypic changes of the epithelium, there is a need for molecular assessment of HNMs. However, molecular studies of HNMs in OSCC are sparse. Recently, molecular strategies such as IHC expression of markers and gene amplification of Loss of Heterozygosity (LOH) of markers by the use of polymerase chain reaction have been studied, and results suggest that they provide useful prognostic information and influence the clinical management.,,,,,,, Studies have shown that subjecting the SMs for molecular analysis helps to determine the adequacy of tumor tissue removal. Overexpression of tumor suppression genes (such as p53 and TP53),,, oncogenes (such as epidermal growth factor receptor), and proto-oncogenes (like Her-2) in margins reported to be cancer free on routine histopathological examination explains the initiation of premalignant and malignant changes at theses margins, which may further result in recurrence and second primary tumors. The summary of the molecular studies on HNMs in OSCC has been depicted in [Table 4].
|Table 4: Summary of studies on tumor-free surgical margins of oral cancer|
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Hence, it seems logical to subject SMs to molecular analysis to predict the prognosis and recurrence so as to improve the quality of life for OSCC patients. However, further studies are required to address the need for assessment of molecular markers from research stance.
| > Summary and Conclusion|| |
Assessment of SMs in OSCC forms an integral part to predict the treatment outcome. Factors such as tumor site, tumor stage, tissue shrinkage, and mucosal elasticity should be taken into consideration while deciding the optimal resection margin. Currently, a 1-cm three-dimensional margin is considered optimal. Patients with positive and close margins should be dealt with caution as they have elevated risk for local recurrence. The close resection margins should be considered separately with regard to prognosis. With availability of numerous techniques, the best suitable method or multimodal diagnostic protocol has to be followed by the surgeons to achieve complete clearance of SMs to improve the morbidity of the patients. The presence of genetic alterations in HNMs demands the refinement of definition of tumor-free margins in OSCC and it is recommended to include molecular status along with histology. This would influence the therapeutic approach and predict local recurrence and survival rate. Beholding the role of theses genetic and molecular alterations to predict recurrence and survival, further studies are recommended that focus on validation and assessment of clinical utility of these molecular markers.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]