Abstract
Depth of Invasion (DOI) is an important and independent predictor for occult metastasis and recurrence. AJCC staging system (8th edition) has incorporated DOI in the staging of oral cancers. It is an essential parameter in deciding elective neck dissection. We hereby conducted a study to determine the accuracy of DOI in the frozen section as compared to the histological section in patients with T1N0 oral squamous cell carcinoma. This study was conducted over a period of 45 months in a tertiary care hospital. 31 patients with diagnosed Oral SCC and with T1N0 were enrolled. The intra-operative frozen section was done DOI was measured as per Cap protocol and compared with the DOI in the histopathological section. Strong correlation was found between DOI measured by frozen section and permanent section (r = 0.998; 95% CI, 0.999–0.997). The paired t test showed a mean difference of 0.0066 mm (95% CI, − 0.0103–0.02346 mm; P = 0.096) between frozen section and permanent section. DOI measured was slightly higher in frozen section however this difference was neither statically nor clinically significant.This study shows the accuracy of frozen specimens in determining tumor DOI in T1N0M0 in oral cavity squamous cell carcinoma. Intraoperative DOI along with other factors may be used to determine the need for END (elective neck dissection) in early-stage oral cavity squamous cell carcinoma and thus avoid a staged operation or over- or under-treatment of the neck.
Keywords: Depth of invasion, DOI, Oral squamous cell carcinoma, SCC, AJCC
Introduction
There is a well-established relationship between the depth of invasion and loco-regional lymphatic metastasis in oral cavity squamous cell carcinoma. Depth of invasion is one of the important predictors of nodal metastasis in oral cavity squamous cell carcinoma [1]. It can facilitate the decision to complete an elective neck dissection in the early-stage disease. Enough studies about the identification of intra-operative depth of invasion in oral cavity squamous cell carcinoma are not done. Identification of depth of invasion postoperatively can lead to delay in the planning of treatment and elective neck dissection in oral cavity squamous cell cancer. Hence it is reasonable to make plans intra-operatively. This can be accomplished with frozen section studies. The purpose of this study is to investigate the accuracy of the depth of invasion on the intra-operative frozen specimen and its comparison with the formalin-fixed specimen for T1N0 oral cavity squamous cell carcinoma.
Materials and Methods
The study was done at our tertiary care hospital between Dec 2015 to Sep 2019. Patients of oral cavity squamous cell carcinoma with clinical-stage T1N0M0 were included in the study. A complete workup of the patients was done before surgery. A detailed clinical examination and PET scan were done before surgery. National Comprehensive guidelines 2018 were followed [2]. All patients underwent surgery on the primary tumor. Frozen section for measurement of the depth of invasion was done in all patients. After orientation of the specimen tumour sized was accessed and surface with largest depth was sectioned using BP Blade. The section selected was placed in the chucks and poured with embedding media. The chuck with tissue and embedding media were kept in the cryostat cabinet. The cryostat cabinet was adjusted to a temperature ranging from − 20 °C to − 25 °C. At this temperature solidification of the embedding media occurs. The plane of the tissue was adjusted and kept parallel to the edge of blade. High profile disposable blades were placed in the blade holder, which is held on a base fixed at 45 degree angulations. After obtaining appropriate section it was stained by rapid Haematoxyline and Eosin. Thickness measurements were made under the light micro- scope by experienced oncopathologist as per CAP protocol. Depth of invasion was measured in millimeters as per the American Joint Committee on Cancer (AJCC) manual. As per AJCC guidelines and cap protocol, DOI was measured from the adjacent normal basement membrane to the point of the deepest invasion of the tumor. A clear scale was used to measure the distance from the normal basement membrane and dropping the plumb line to the deepest. The difference between the depth of invasion intra-operatively and postoperatively on histopathological section was studied. Cut off value for depth of invasion for elective neck dissection was taken as 5 mm for all oral cavity squamous cell carcinoma based on AJCC guidelines (8 edition).
Statistical Analysis
Statistical analysis was done on XL-stat statistical software. The difference between the frozen and the histopathological sections was studied by paired t-test. To assess the correlation Pearson correlation coefficients along with 95% CI were calculated. Statistical significance was defined as P < 0.05.
Result
31 patients were included in the study. Their age ranged from 48 to 71 years. All patients were clinically staged as T1N0M0. All patients were of primary squamous cell carcinoma of the oral cavity. The oral cavity sub sites were as follows—21cases of carcinoma tongue, 04 cases of the gingivobuccal sulcus and 06 cases of the floor of mouth. Clinical details of the patients are listed in Table 1. A total of 3 patients (10.7%) underwent an elective neck dissection based on depth of invasion in frozen sections of tissue report. Out of these 2 patients had a depth of invasion of equal toto more than 5 mm. One patient with DOI as 4.8 mm also underwent END. Depth of invasion was approximately the same in all cases in permanent histopathological sections and in the frozen section (Table 1) except two cases where the difference in depth of invasion was noted but it was less than 2 mm. There was no discrepancy between the depth of invasion in frozen specimens and permanent tissue sections. 28 cases (90.3%) did not undergo END based on frozen section depth of invasion. These patients were not under-treated based on DOI in permanent specimens.
Table 1.
Clinical profile and the measured depth of invasion intraoperative and postoperative
| Serial number | Age | Sex | Tumor Site | Clinical Stage | Depth of Invasion in mm (Intra Operative) | Depth of Invasion (Post Operative) |
|---|---|---|---|---|---|---|
| 1 | 48 | M | Tongue | T1N0M0 | 1.5 | 1.5 |
| 2 | 54 | M | Tongue | T1N0M0 | 1.2 | 1.1 |
| 3 | 63 | M | Tongue | T1N0M0 | 5 | 5 |
| 4 | 67 | M | Tongue | T1N0M0 | 3 | 3 |
| 5 | 57 | F | Tongue | T1N0M0 | 4.2 | 4.2 |
| 6 | 60 | M | Tongue | T1N0M0 | 3 | 2.8 |
| 7 | 63 | F | Tongue | T1N0M0 | 2 | 2 |
| 8 | 71 | M | Tongue | T1N0M0 | 1.4 | 1.4 |
| 9 | 64 | M | Tongue | T1N0M0 | 2.1 | 2.1 |
| 10 | 68 | F | Tongue | T1N0M0 | 3.1 | 3.1 |
| 11 | 56 | M | Tongue | T1N0M0 | 2.7 | 2.7 |
| 12 | 63 | M | Tongue | T1N0M0 | 4.8 | 4.8 |
| 13 | 69 | F | Tongue | T1N0M0 | 2.2 | 2.2 |
| 14 | 59 | M | Tongue | T1N0M0 | 2 | 2 |
| 15 | 63 | M | Tongue | T1N0M0 | 1.60 | 1.60 |
| 16 | 49 | M | Tongue | T1N0M0 | 3.80 | 3.80 |
| 17 | 56 | F | Tongue | T1N0M0 | 2.70 | 2.70 |
| 18 | 68 | M | Tongue | T1N0M0 | 2.3 | 2.3 |
| 19 | 68 | F | Tongue | T1N0M0 | 1.7 | 1.7 |
| 20 | 55 | M | Tongue | T1N0M0 | 2.2 | 2.2 |
| 21 | 55 | M | Tongue | T1N0M0 | 1.5 | 1.5 |
| 22 | 59 | M | Gingivobuccal sulcus | T1N0M0 | 3.2 | 3 |
| 23 | 56 | F | Gingivobuccal sulcus | T1N0M0 | 2 | 2 |
| 24 | 59 | F | Gingivobuccal sulcus | T1N0M0 | 1.6 | 1.6 |
| 25 | 60 | M | Gingivobuccal Sulcus | T1N0M0 | 1 | 1 |
| 26 | 59 | M | Floor of mouth | T1N0M0 | 1.5 | 1.5 |
| 27 | 70 | M | Floor of mouth | T1N0M0 | 2 | 2 |
| 28 | 66 | M | Floor of mouth | T1N0M0 | 1.5 | 1.5 |
| 29 | 48 | M | Floor of mouth | T1N0M0 | 5.2 | 5.2 |
| 30 | 53 | M | Floor of mouth | T1N0M0 | 2.2 | 2.2 |
| 31 | 58 | M | Floor of mouth | T1N0M0 | 2.7 | 2.7 |
Strong correlation was found between DOI measured by frozen section and permanent section (r = 0.998; 95% CI, 0.999–0.997). The paired t test showed a mean difference of 0.0066 mm (95% CI, − 0.0103–0.02346 mm; P = 0.096) between frozen section and permanent section. DOI measured was slightly higher in frozen section however this difference was neither statically nor clinically significant.
Discussion
Treating clinically node-negative neck inT1N0M0 oral cavity carcinoma is always a challenge. It is a complex decision requiring a multidisciplinary approach. Depth of invasion is an important prognostic marker in oral cavity malignancies. National Comprehensive Cancer Network guidelines 2018 included depth of invasion as an important marker for deciding elective neck node dissection. DOI is the important marker for predicting nodal metastasis, hence can be used in deciding factor for elective neck dissection. Importance of depth of invasion is studied in various malignancies like melanoma, basal cell carcinoma of the skin and oral cavity carcinoma [3, 4]. This study is carried out to evaluate the accuracy of the depth of invasion measurement in oral cavity squamous cell carcinoma. In this study, intra-operative depth of invasion is shown to be accurate in deciding whether the patient should undergo elective neck dissection or not. Two important predictors for nodal metastasis are tumor thickness and depth of invasion. Various studies are conducted in the past to study the role of tumor thickness and depth of invasion in oral cavity carcinomas. Tumor thickness is the distance from the mucosal surface to the deepest point of tumor invasion [5].
Cases with surface ulceration, a reconstructed mucosal line at the level of the adjacent intact mucosal surface can be used for determining tumor thickness. According to the eighth edition of the AJCC guidelines, tumor depth is the distance from the basement membrane to the deepest point of invasion [6]. The difference between the depth of invasion and tumor thickness has been studied in the past in various studies [7]. The reported depth of invasion which would warrant a neck dissection ranges from 1.5 to 10 mm, with 2 to 5 mm most often being cited in various studies [8]. In our study cut off for elective neck dissection was 5 mm based on recent NCCN guidelines.
A retrospective cohort study of 927 patients was done and it was found that only 5.7% of patients had a different T category according to the eighth edition of the AJCC guidelines when the thickness was used instead of depth of invasion [8].
Our study suggests that there is a high degree of concordance for DOI measurement in frozen versus permanent pathology sections. Studies have reported the link between tumor thickness or depth and overall survival and DSS.
Retrospective review of 29 patients with T1 to T2 squamous cell carcinoma of the tongue or floor of the mouth concluded that greater tumor thickness is associated with delayed regional metastasis, with a value of 2.2 mm as the cutoff for elective neck. dissection [9]. A retrospective study of 246 patients with T1N0–T2N0 disease concluded that depth of invasion is an independent prognostic factor of nodal involvement, with a recommended cutoff of 4 mm for elective neck dissection [10]. A randomized control trial of 500 patients was done in 2015. Patients with clinical stage T1N0 and T2N0 were included in the study. They concluded that there was overall survival benefit and a delayed recurrence when elective neck dissection was done at the time of ablative surgery. Elective neck dissection for T2 tumors is generally indicated but T1 tumors comprise the group for which the dilemma for elective neck dissection arises. The authors stated that DOI has limited applicability as it was not feasible to perform DOI measurement before or at the time of primary surgery [11]. Our study provides data that suggest that DOI in frozen sections can be relied on for intra-operative decision making and, therefore, a single-step surgical procedure can be completed that is appropriately determined by DOI. In this study, frozen specimens correlated with permanent specimens and there was no relevant difference found.
Conclusion
This study shows the accuracy of frozen specimens in determining tumor DOI in cT1N0M0 in oral cavity squamous cell carcinoma. Intra-operative DOI along with other factors may be used to determine the need for END in early-stage oral cavity squamous cell carcinoma and thus avoid a staged operation or over- or under-treatment of the neck.
Funding
There is no financial support for this work that could have influenced its outcome.
Compliance with Ethical Standards
Conflict of interest
The authors declare that they have no conflict of interest.
Footnotes
Publisher's Note
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References
- 1.Kane SV, Gupta M, Kakade AC, D’Cruz A. Depth of invasion is the most significant histological predictor of subclinical cervical lymph node metastasis in early squamous cell carcinomas of the oral cavity. Eur J Surg Oncol. 2006;32:795. doi: 10.1016/j.ejso.2006.05.004. [DOI] [PubMed] [Google Scholar]
- 2.Ettinger DS, Aisner DL, Wood DE, Akerley W, Bauman J, Chang JY, Chirieac LR, DAmico TA, Dilling TJ, Dobelbower M, Govindan R. NCCN guidelines insights: non–small cell lung cancer, version 52018. J Nat Compr Cancer Netw. 2018;1(16):807–21. doi: 10.6004/jnccn.2018.0062. [DOI] [PubMed] [Google Scholar]
- 3.Kiehl P, Matthies B, Ehrich K, et al. Accuracy of frozen section measurements for the determination of breslow tumour thickness in primary malignant melanoma. Histopathology. 1999;34:257. doi: 10.1046/j.1365-2559.1999.00621.x. [DOI] [PubMed] [Google Scholar]
- 4.Frierson HF, Jr, Cooper PH. Prognostic factors in squamous cell carcinoma of the lower lip. Hum Pathol. 1986;17:346. doi: 10.1016/S0046-8177(86)80457-9. [DOI] [PubMed] [Google Scholar]
- 5.Edge SB, Byrd DR, Compton CC, editors. AJCC Cancer staging manual. New York: Springer; 2010. [Google Scholar]
- 6.Ydiatt WM, Shah JP, Hoffman HT, et al. AJCC stage groupings for head and neck cancer: should we look at alternatives? a report of the head and neck sites task force. Head Neck. 2001;23:607. doi: 10.1002/hed.1086. [DOI] [PubMed] [Google Scholar]
- 7.Dirven R, Ebrahimi A, Moeckelmann N, et al. Tumor thickness versus depth of invasion analysis of the 8th edition American joint Committee on cancer staging for oral cancer. Oral Oncol. 2017;74:30. doi: 10.1016/j.oraloncology.2017.09.007. [DOI] [PubMed] [Google Scholar]
- 8.International Consortium for Outcome Research (ICOR) in Head and Neck Cancer, Ebrahimi A, Gil Z, Amit M et al. (2014) Primary tumor staging for oral cancer and a proposed modification incorporating a depth of invasion: An international multicenter retrospective study. JAMA Otoloaryngol Head Neck Surg. 140: 1138 [DOI] [PubMed]
- 9.Warburton G, Nikitakis NG, Roberson P, et al. Histopathological and lymphangiogenic parameters in relation to lymph node metastasis in early stage oral squamous cell carcinoma. J Oral Maxillofac Surg. 2007;65:475. doi: 10.1016/j.joms.2005.12.074. [DOI] [PubMed] [Google Scholar]
- 10.Melchers LJ, Schuuring E, van Dijk BA, et al. Tumour infiltration depth ≥4 mm is an indication for an elective neck dissection in pT1cN0 oral squamous cell carcinoma. Oral Oncol. 2012;48:337. doi: 10.1016/j.oraloncology.2011.11.007. [DOI] [PubMed] [Google Scholar]
- 11.D’Cruz AK, Vaish R, Kapre N, et al. Elective versus therapeutic neck dissection in node-negative oral cancer. N Engl J Med. 2015;373:521. doi: 10.1056/NEJMoa1506007. [DOI] [PubMed] [Google Scholar]