[960] p16INK4a Staining Characteristics in Endometrioid Endometrial Adenocarcinoma; Information Useful When Establishing Cervical or Endometrial Origin
CM Davidson, PL Farmer, TJ Childs. Queen's University/Kingston General Hospital, Kingston, ON, Canada
Background: Distinguishing endometrioid adenocarcinomas arising from cervix from those arising from uterus is clinically important as therapeutic options vary with site-of-origin. Markers commonly applied in this scenario include ER, vimentin , CEA and more recently p16INK4a. Tumours from the cervix typically exhibit moderate to strong p16 staining in the majority of tumour cells. Conversely, less than half of tumour cells from endometrial tumours stain, often with lower intensity. A detailed description of p16 staining across histologic grade and architectural pattern (glandular, solid and squamous) has, to our knowledge, not been reported. Of particular interest, since biopsies are often small, were the proportion of strongly staining glands and the size of foci exhibiting solid, intense staining, as these features may introduce diagnostic uncertainty.
Design: 33 randomly selected well, moderately, and poorly differentiated endometrioid endometrial carcinomas in hysterectomy specimens were screened and representative tissue blocks were identified (n=32, 32 and 29, respectively). Sections were stained with p16 antibody (16PO4). The intensities of p16 staining within glandular, solid and squamous components were scored. The percent of glands comprised exclusively of strong staining cells and the length of largest staining focus were also recorded.
Results: Overall, 43% of tumour cells did not stain for p16. Squamous areas had a larger proportion of cells staining with moderate or strong staining than did glandular areas (53% vs 39%, p<0.05). A trend toward stronger staining in high grade tumours (p=0.085, ns) was noted. High grade tumours more frequently had 
10% of glands with exclusively strong staining cells (6/29) versus well (0/32) and moderately (2/32) differentiated tumours, and also more frequently had solid staining foci measuring >2mm (9/29 versus 0/32 and 3/32, respectively).
Conclusions: 1) 57% of tumour cells stained for p16 while 43% did not. 2) Albiet by a small degree, squamous areas stained for p16 more intensely than did glandular areas. 3) There was a non-significant trend of stronger p16 staining in high grade tumours. 4) When trying to distinguish the site of origin (cervical versus endometrial) on scanty biopsies / currettings, the presence of solid, strong foci of p16 staining or strong staining in 10% of glands may be consistent with an endometrial primary if other evidence is supportive.
Category: Gynecologic
Monday, March 9, 2009 9:30 AM
Poster Session I Stowell-Orbison/Autopsy Award # 145, Monday Morning