Table 1 Baseline characteristics of study population according to metformin use
Co-variate | Full Sample (n = 329) | Non-Metformin (n = 134) | Metformin (n = 195) | p-value |
|---|---|---|---|---|
Primary Site (%) | 0.71 | |||
 Oral cavity | 117 (36) | 49 (37) | 68 (35) |  |
 Oropharynx | 80 (24) | 36 (27) | 44 (23) |  |
 Hypopharynx | 13 (4) | 5 (4) | 8 (4) |  |
 Larnyx | 119 (36) | 44 (33) | 75 (38) |  |
Age | 0.9 | |||
 Mean (sd) | 67.4 (9.7) | 67.6 (9.7) | 67.3 (9.8) |  |
 Median (Min,Max) | 67.9 (40.9,89.9) | 68.3 (42.6, 89.9) | 67.6 (40.9, 89.6) |  |
Treatment Modality (%) | 0.67 | |||
 Surgery | 73 (22) | 30 (22) | 43 (22) |  |
 Adjuvant Rad | 38 (12) | 14 (10) | 24 (12) |  |
 Adjuvant Chemo/Rad | 8 (2) | 1 (1) | 6 (3) |  |
 Primary Rad | 159 (48) | 66 (49) | 93 (48) |  |
 Primary Chemo/Rad | 52 (16) | 23 (17) | 29 (15) |  |
Extracapsular spread (%) | 0.04* | |||
 Absent | 52 (84) | 24 (96) | 28 (76) |  |
 Present | 10 (16) | 1 (4) | 9 (24) |  |
 Missing | 267 | 109 | 158 |  |
Perineural invasion (%) | 0.49 | |||
 No | 47 (59) | 22 (65) | 25 (56) |  |
 Yes | 32 (41) | 12 (35) | 20 (44) |  |
 Missing | 250 | 100 | 150 |  |
CCI (%) | < 0.001* | |||
 0 | 9 (3) | 9 (7) | 0 (0) |  |
 1 | 186 (57) | 61 (46) | 125 (64) |  |
 2 | 78 (24) | 36 (27) | 42 (22) |  |
 3+ | 56 (17) | 28 (21) | 28 (14) |  |
Smoking (%) | 0.69 | |||
 Never | 74 (23) | 32 (24) | 42 (22) |  |
 Current/Ex | 252 (77) | 101 (76) | 151 (78) |  |
 Missing | 3 | 1 | 2 |  |
Drinking (%) | 0.029* | |||
 Never/Light | 188 (63) | 67 (55) | 121 (68) |  |
 Moderate/Heavy/Ex | 111 (37) | 54 (45) | 57 (32) |  |
 Missing | 30 | 13 | 17 |  |
Clinical Stage (%) | 0.91 | |||
 Early 0/I/II | 133 (41) | 54 (41) | 79 (42) |  |
 Late III/IV | 190 (59) | 79 (59) | 111 (58) |  |
 Missing | 6 | 1 | 5 |  |
Stage cN (%) | 0.42 | |||
 N0/Nx | 190 (59) | 77 (58) | 113 (59) |  |
 N1 | 23 (7) | 7 (5) | 16 (8) |  |
 N2 | 100 (31) | 46 (35) | 54 (28) |  |
 N3 | 11 (3) | 3 (2) | 8 (4) |  |
 Missing | 5 | 1 | 4 |  |
Stage cT (%) | 0.63 | |||
 T0/Tx | 1 (0) | 0 (0) | 1 (1) |  |
 T1 | 81 (25) | 28 (22) | 53 (28) |  |
 T2 | 101 (32) | 45 (35) | 56 (29) |  |
 T3 | 77 (24) | 33 (25) | 44 (23) |  |
 T4a/4b | 60 (19) | 24 (18) | 36 (19) |  |
 Missing | 9 | 4 | 5 |  |
Staging cM (%) | 0.52 | |||
 M0 | 327 (99) | 134 (100) | 193 (99) |  |
 M1 | 2 (1) | 0 (0) | 2 (1) |  |
Follow-up time | 0.69 | |||
 Mean (sd) | 3.1 (2.1) | 3 (2.2) | 3.1 (2.1) |  |
 Median (Min, Max) | 2.7 (0,8.8) | 2.7 (0,8.8) | 2.8 (0,8.4) |  |