Effect of CEACAM6 overexpression on tumour initiation. A) Varying numbers of control (PLV101 control) or CEACAM6 overexpressing (PLV101 CEA) Detroit cells were assayed for their ability to initiate tumours in NOD/SCID mice. Mice (6/group) were monitored over a 12 week period and the incidence of tumours and the time till tumours were palpable is recorded. B) CEACAM6, PCNA and cleaved Caspase 3 expression was determined immunohistochemically at 4x and 20x magnification in xenotransplant tumours derived from pLV101 control and pLV101 CEACAM6 over-expressing cells (insets are IgG control sections). C, D) PCNA positivity in the CEACAM6 over-expressing and control tumours was estimated as the number of positive cells per 100 cells in a field of view by NIS-Elements BR3.1 imaging software. Quantification of cleaved caspase 3 expression (D) was estimated as number of positive cells per field of view by NIS-Elements BR3.1 imaging software. All data expressed as mean +/− sem. * P ≤ 0.05.