Patients and pathological examinations

The records of 89 patients who underwent radical surgery for previously untreated OTSCC between January 2001 and December 2011 were reviewed retrospectively. The study cohort included patients with histologically confirmed OTSCC and a minimum follow-up of 12 months. All study patients underwent extensive pre-treatment evaluations, including blood chemistry, complete blood cell count, chest X-ray, computed tomography (CT) and/or magnetic resonance imaging (MRI) of the head and neck area, ultrasonic echo (US), and thoraco-abdominal CT, and provided informed consent to participate in the study. During the study period, surgery alone was preferred for the initial treatment of patients with oral cancer in our institution. However, patients who were unwilling to consent to a surgical intervention and inoperable patients with unresectable cancer and/or a severe systemic illness were selected for chemotherapy, radiation therapy, and/or supportive palliation.

All patients underwent glossectomy with curative intent. A neck dissection was performed for the clinical node (cN)-positive cases and cN-negative cases who required tongue reconstructive surgery because of the size of the primary tumour. No sentinel lymph node biopsy was performed. Postoperative adjuvant chemo/radiotherapy or RT was applied in accordance with the current National Comprehensive Cancer Network (NCCN) guidelines. Patients who had adverse features (high risk features including extracapsular nodal spread and the presence of positive margins; intermediate risk features including multiple positive nodes without extracapsular nodal spread, perineural/vascular invasion, pT3/T4 primary tumours, and positive level IV/V nodes) were treated depending on the degree of the risk. Clinical staging was defined by palpation, inspection, CT, MRI, US, etc., according to the Union for International Cancer Control (UICC) TNM classification system.

Tumours were classified histopathologically as well-, moderately, or poorly differentiated according to their cellular differentiation, as defined by the UICC. The pattern of invasion was examined at the host/tumour interface; pattern of invasion types 1–4 were defined previously by Bryne et al. The depth of invasion was measured as the infiltrative portion of the tumour that extended below the surface of the adjacent mucosa. Previous studies have demonstrated that a depth of invasion ≥4 mm has predictive value for cervical lymph node metastasis in patients with OTSCC ; therefore, depth of invasion was classified as ≥4 and <4 mm in the current study. A previous large cohort study demonstrated that a pathological margin distance ≤4 mm was significantly associated with loco-regional recurrence ; therefore, surgical margin status was classified as superficial (>4 mm) and deep (≤4 mm) in this study.

Perineural invasion was defined as the presence of tumour cells within any of the three layers of the nerve sheath (the epineurium, perineurium, and endoneurium). Vascular invasion was defined as the clear presence of tumour cells within a vascular space (lymphatic space or blood vessel), and it was required that the tumour be adhered to the vessel endothelium or attached to a thrombus in the vessel. Expert pathologists who were unaware of the clinical outcomes performed all pathological assessments. Disease-specific survival (DSS) was calculated from the time of initial examination to the time of death related to local, regional, or distant recurrence/metastasis of the disease or the time of last follow-up. Overall survival (OS) was calculated from the time of initial examination to the time of death or last follow-up.

Statistical analysis

Statistical analyses were performed using StatMate IV (ATMS Co. Ltd, Tokyo, Japan). Categorical data were assessed using the χ ² test or Fisher’s exact test, as appropriate. The clinicopathological information related to perineural/vascular invasion was compared using the χ ² test or Fisher’s exact test, as appropriate. The clinicopathological information included pT stage, histopathological nodal status, UICC stage, pattern of invasion, local recurrence, and treatment. DSS and OS were calculated using the Kaplan–Meier method, and significance was evaluated using the log-rank test. A value of P < 0.05 was considered to be significant.

Patient characteristics

The demographic and clinical characteristics of the study patients are summarized in Table 1 . The male-to-female ratio was 1.28; 50 subjects were male. The mean age at diagnosis was 63.4 years (range 28–88 years). Perineural invasion was found in 24 of 89 patients (27.0%), and vascular invasion in 21 (23.6%). Histopathological lymph node metastasis was found in 25 (28.1%) patients. Local recurrence developed in 11 patients (12.4%) during the follow-up period. Postoperative distant metastasis occurred in three (3.4%) patients. The mean follow-up period of the whole series was 49.4 months (range 3–125 months).

Association of perineural invasion with clinicopathological factors and survival

Perineural invasion was associated significantly with the T-classification, histopathological nodal status, pattern of invasion, depth of invasion, and distant metastasis, but not with local recurrence ( Table 2 ). Univariate analysis using the two-tailed Fisher’s exact test revealed that perineural invasion had a strong relationship with the T-classification ( P = 0.02), histopathological nodal status ( P = 0.005), UICC stage ( P = 0.002), pattern of invasion ( P < 0.001), depth of invasion ( P < 0.001), and distant metastasis ( P = 0.02).

Table 2

Associations of perineural/vascular invasion with clinicopathological factors.

	Perineural invasion			Vascular invasion
	Yes	No	P -Value	Yes	No	P -Value
Gender			NS			NS
Male	12	38		13	37
Female	12	27		8	31
Age, years			NS			NS
≥64	12	36		11	37
≤63	12	29		10	31
pT stage			0.02			NS
T1 + T2	19	63		18	64
T3 + T4	5	2		3	4
Histopathological nodal status			0.005			0.005
No metastasis	12	52		10	54
Metastasis	12	13		11	14
UICC stage			0.002			NS
I, II	14	58		14	58
III, IV	10	7		7	10
Pattern of invasion			<0.001			NS
1 + 2 + 3	12	59		14	57
4	12	6		7	11
Depth of invasion			<0.001			0.01
<4 mm	4	51		8	47
≥4 mm	20	14		13	21
Local recurrence			NS			NS
No	19	59		18	60
Yes	5	6		3	8
Distant metastasis			0.02			NS
No	21	65		21	65
Yes	3	0		0	3
Disease-specific survival			<0.001			NS
Alive	15	63		16	62
Dead	9	2		5	6
Overall survival			0.002			NS
Alive	15	60		16	59
Dead	9	5		5	9

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