1

Supplementary Table S1. Characteristics of 186 clinical specimens assessed by GCS and P-pg immunohistochemistry

Characteristic / N / %
Sex (men/women) / 112/74 / 60.2/39.8
Age [years, median (range)] / 60 (29–95)
Smoking (pack-years, <20/≥20) / 110/76 / 59.1/40.9
Alcohol (drinks per day, <1/≥1) / 152/34 / 81.7/18.3
Primary site
Tongue / 139 / 74.7
Buccal / 16 / 8.6
Mouth floor / 14 / 7.5
Gingiva / 7 / 3.8
Retromolar trigon / 5 / 2.7
Hard palate / 4 / 2.2
Lip / 1 / 0.5
Tumor grade (G1/G2/G3) / 111/58/17 / 59.7/31.2/9.1
Tumor size [cm, median (range)] / 2.2 (0.5–7.0)
Tumor depth of invasion / 0.8 (0.1–4.0)
Resection margin, clear/close/positive / 117/54/15 / 62.9/29.0/8.1
pTNM stage
T1/T2/T3/T4 / 76/80/9/21 / 40.9/43.0/4.8/11.3
N0/N1/N2/N3 / 102/33/51/0 / 54.8/17.7/27.4/0.0
I/II/III/IV / 57/33/35/61 / 30.6/17.7/18.8/32.8
Primary treatment
Primary resection + ipsilateral/bilateral ND / 162/24 / 87.1/12.9
Postoperative RT/CRT / 80/8 / 43.0/4.3
Follow-up information
Median (range) period (months) / 74 (16–168)
Recurrencea / 65 / 34.9
Overall/cancer-specific death / 78/57 / 41.9/30.6

Abbreviations: CRT, concurrent chemoradiation therapy; ND, neck dissection; RT, radiation therapy; pTNM, pathological tumor-node-metastasis stage (American Joint Committee on Cancer, 7th ed.).

aRecurrences includes all locoregional recurrences and distant metastases during follow-up.

1

Supplementary Table S2. Relationship between GCS and P-gp expression

Expression / GCS, low / GCS, high / Total / Level of significance
P-gp, negative / 52 / 91 / 143 / P = 0.005
P-gp, positive / 6 / 37 / 43
Total / 58 / 128 / 186

Abbreviations: GCS, glucosylceramide synthase; P-gp, P-glycoprotein.

1

Supplementary Table S3. Role of P-glycoprotein and glucosylceramide synthase in defining prognosis in head and neck cancer

Author / Year / Total no. / Tumor site / Pathology / Primary treatment / P-gp expression / Ancillary marker / Prognostic role / Method
P-glycoprotein
Rabkin et al.24 / 1995 / 33 / Tongue base / SCC / NoD / 33/33 (100%) / – / Shorter OSa / IHC
Ralhan et al.12 / 1999 / 100 / OC / SCC / NoD / 81/100 (81%) / p53 / Shorter DFS / IHC
Warnakulasuriya et al.25 / 2000 / 111 / OC (21), OP (25), HP (9), NS (7), NP (4), Lx (2) / SCC, III / RT + Cb / 69/111 (62%) / p53 / Shorter DFS, OS / IHC
Uematsu et al.26 / 2001 / 46 / OC (37), SG (9) / SCC, ACC, AC / NoD / 12/37 (32%, OC), 9/9 (SG) / – / NoD / IHC
Soni et al.27 / 2002 / 40 / OC / SCC / S + RT / 27/40 (68%) / p53, Ets-1 / Shorter DFS / IHC
Friedrich et al.28 / 2004 / 45 / OC (34), OP/HP (6), Lx (4), recurrence (1) / SCC / NoD / 8/45 (8%) / MRP-1 / No association / IHC, qRT-PCR
Larbcharoensub et al.29 / 2008 / 60 / NP / II, III / CRT / 2/60 (3%) / MRP-1 / No association / IHC
Li et al.13 / 2011 / 86 / Lx / SCC / S ± RT / 34/86 (40%) / Survivin / LNM, shorter OS / IHC
Furusaka et al.30 / 2013 / 13 / Parotid gland / MEC / S / 8/13 (62%) / – / HG, recurrence / IHC
Warta et al.31 / 2014 / 40 / OP (21), HP (11), OC (5), Lx (3) / SCC / NoD / mRNA expression / MRP1 / Longer PFS, OS / qRT-PCR
Present study / 2015 / 186 / OC / SCC / S ± RT/CRT / 43/186 (23%) / GCS / Shorter LRC, DFS, OS / IHC
Glucosylceramide synthase
Previously not tested in patients with head and neck cancer
Present study / 2015 / 186 / OC / SCC / S ± RT/CRT / 128/186 (69%) / P-gp / Shorter LRC, DFS / IHC

Abbreviations: AC, adenocarcinoma; ACC, adenoid cystic carcinoma; CRT, concurrent chemoradiotherapy; DFS, disease-free survival; GCS, glucosylceramide synthase; HG, predict high histological grade; HP, hypopharynx; IHC, immunohistochemistry; LNM, predict cervical lymph node metastasis; LRC, locoregional control; Lx, larynx; MEC, Mucoepidermoid carcinoma; MRP-1, multidrug resistance-associated protein 1; NP, nasopharynx; NoD, not defined; NS, nasal sinus; OC, oral cavity; OP, oropharynx; OS, overall survival; PFS, progression-free survival; qRT-PCR, quantitative reverse transcription polymerase chain reaction; RT, radiotherapy; S, surgery; SCC, squamous cell carcinoma; II and III, World Health Organization (WHO) classification systems; SG, salivary gland.

a Higher expression showed the trend for decreased survival.

b Patients had unresectable stage III or IV cancers and underwent radiotherapy with synchronous or sequential chemotherapy.