The histopathology archive represents a vast, well-characterized source of specimens covering virtually every disease and is available for molecular biological investigation. The archive has in recent years become widely used for molecular genetic analysis and DNA can be routinely extracted from formalin-fixed, paraffin-embedded tissue. More recently, archival specimens have become a source of material for extensive analysis of mRNA expression utilizing DNA microarrays, real-time quantitative reverse transcriptase polymerase chain reaction (PCR), and in situ hybridization and amplification techniques. These techniques will enable a greater understanding of the changes that occur in gene function during every stage of the development of disease and will lead to better diagnosis, better evaluation of prognosis, and better treatment through targeted therapeutic regimes.

Achaete-scute like (ASCL)2 is a basic helix-loop-helix transcription factor essential for the maintenance of proliferating trophoblasts during placental development. Using oligonucleotide microarrays we identified ascl2 as a gene significantly upregulated in colorectal adenocarcinomas (n ¼ 36 cancers, n ¼ 16 normals; 15-fold, Po0.0001). This finding was confirmed by quantitative reverse transcriptase (RT)-PCR on large intestinal cancers (n ¼ 29 cancers, n ¼ 16 normals; 10-fold, Po0.0001).In situ hybridization for ascl2 demonstrated expression at the base of small and large intestinal crypts (n ¼ 304), but in no other normal tissues excepting placenta. By in situ hybridization, 52-71% of colorectal adenomas (n ¼ 187), 50-73% of large (n ¼ 327) and 33-64% of small intestinal adenocarcinomas (n ¼ 124) were positive for ascl2 expression. Upregulation of murine ascl2 was also observed using oligonucleotide microarrays, quantitative RT-PCR and in situ hybridization on apc min/ þ and apc 1638N/ þ smad4 À/ þ tumours. Tumour cell lines stably transfected with LEF1 DN or APC2, or transiently transfected with short-interfering RNA (siRNA) against b-catenin showed a significant downregulation of ascl2. Colocalization of ascl2 with nuclear b-catenin was observed in 73 small intestinal adenocarcinomas (P ¼ 0.0008) and apc min/ þ tumours. Preliminary in vitro data suggest ascl2 may promote progression through the G2/M cell cycle checkpoint. In summary, ascl2 is a putative regulator of proliferation that is overexpressed in intestinal neoplasia.

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Variations in nodal yield are due to idiosyncratic patient and tumor characteristics and differences in the quality of surgery and pathology undertaken. Adequate lymphadenectomy is essential to ensure correct stage allocation and optimal survival.