In vivo tumour growth analysis of SP and non-SP (NSP) cells isolated from HK1 NPC cell line. (A) SP or NSP cell inoculation in nude mice. Distinct difference in tumour latency was observed in the lowest inoculated cell number (10 cells). (B) Limiting dilution analysis of SP and NSP tumours. Tumour-initiating cells (TICs) were similarly enriched in both SP and NSP cells (p > 0.05). (C) Representative gross morphology of tumours inoculated with (i) 1000 SP cells, (ii) 1000 NSP cells, (iii) 100 SP cells, (iv) 100 NSP cells, (v) 10 SP cells and (vi) 10 NSP cells. (D) H & E photos of tumours after inoculated into nude mice with (i) unsorted HK1 cells, (ii) SP cells and (iii) NSP cells. Tumours derived from SP and NSP cells showed similar histomorphology to unsorted HK1 cells (black arrowhead pointing to squamous carcinoma; long arrow pointing to keratinization). (iv) A SP cell derived tumour showed vascular invasion (white arrowhead pointing to the invasion of SP cells into a blood vessel). All photos at original magnification 400X.