[1659] Grading of Ileal Carcinoid Tumours Is a Ki-67 Proliferation Index Necessary?

SM Phelan, G Tamagno, R Geraghty, D O'Shea, J Geoghegan, D Maguire, O Traynor, K Sheahan. St. Vincent's University Hospital, Dublin, Ireland

Background: Our ability to predict the behaviour of gastrointestinal carcinoid tumours is limited. Attempts have been made to identify factors associated with outcome to more accurately identify patients at risk of disease progression. One proposed marker is the proliferation index, quantified by immunohistochemistry (IHC), using Ki-67. Criteria for the staging and grading of carcinoid tumours of the mid and hindgut were recently established by the European Neuroendocrine Tumour Society (G. Rindi et al. Virchows Arch 2007). The proposed grading system is three-tiered: G1:<2mitoses/10HPF and/or Ki-67 index<2% G2: 2-20 mitoses/ 10 HPF and/or Ki-67 index between 2 and 20% G3: >20 mitoses/10 HPF and Ki-67 index >20% Few studies have examined the relationship between Ki-67 and mitotic count in ileal carcinoids.
Design: Nineteen ileal carcinoids were identified. Ki-67 IHC was performed on a representative paraffin block. The proliferation index was assessed in 2,000 tumour cells in areas of highest nuclear labelling (Hot-spots). A mitotic count per 10 HPF was performed in areas of greatest mitotic activity on the same H&E stained slide.
Results: 11 patients were female, 8 were male. Patient ages ranged from 39-78 years (mean=63 years). Ki-67 proliferation index was found to correlate with mitotic count using a Spearman test, (r=0.75), p <0.0001. The tumour grade was not altered in any case by Ki-67 staining. Using the proposed grading system, eight tumours were grade 1, 10 were grade 2 and none were grade 3. The Ki-67 proliferation index ranged from 0-293/2000 cells (0-15%) and the mitotic count ranged from 0-15/10HPF. No correlation was found between the Ki-67 index and tumour size or lymph node positivity.
Conclusions: In this patient population with ileal carcinoid tumours, Ki-67 strongly correlated with mitotic count. Tumour grade was not altered by Ki-67 staining in any case. Given that there were no grade 3 tumours, a two-tier grading system may be more appropriate. The quality of pathology reporting may not be improved by Ki-67 IHC as mitotic count is an adequate surrogate marker of proliferation.
Category: Quality Assurance

Monday, March 9, 2009 1:00 PM

Poster Session II # 239, Monday Afternoon