Objective: Message and protein expression of CgA was examined to evaluate the sensitivity of a PCR-based approach in the detection of covert neuroendocrine (NE) tissue.
Summary background data: Immunohistochemical (IHC) measurement of chromogranin A (CgA) discriminates gastrointestinal (GI) carcinoids from epithelial tumors. IHC is, however, an insensitive technique to identify micrometastases or delineate subpopulations of NE cells.
Methods: CgA gene expression was examined by Q-RT PCR in GI carcinoids (small intestinal and metastases, n=17, gastric, n=5), appendiceal tumors (n=10), and adenocarcinomas (gastric, n=5, colorectal, n=6). CgA protein expression levels were quantitatively analyzed following IHC by automated quantitative analysis (AQUA) in 2 tissue microarrays (GI carcinoid and GI adenocarcinoma).
Results: CgA gene was overexpressed (P<0.001) in GI carcinoids compared with GI adenocarcinomas and normal mucosa. Elevated levels (P<0.00001) were also identified in carcinoid liver and lymph node (LN) metastases. CgA levels were higher (approximately 2-4-fold) in NE appendiceal carcinoids than in adenocarcinoids, but in GI adenocarcinomas were identical to normal mucosa. Histologically normal lymph nodes expressed detectable CgA message in 30% of cases. CgA protein levels were highest in primary GI carcinoids and in liver metastases and significantly elevated (P<0.005) compared with nonmetastatic lesions. Expression in liver and LN metastases was significantly elevated (P<0.000001) compared with normal. Analysis of mRNA by Q-RT PCR was >200-fold more sensitive than by IHC.
Conclusions: Overexpression of CgA mRNA and protein in GI carcinoids can identify metastatic cells; thus, PCR for CgA can be used to identify micrometastases not evident by light microscopy or IHC as well as define tumors of ambivalent morphologic phenotype. The use of this sensitive strategy to assess NETs and apparently normal LNs and liver may be of future utility in defining therapeutic strategy.