[1110] Omental Icing: An Unusual Variant of Peritoneal Carcinomatosis Due to Metastatic Gastric or Breast Cancer

CA Jimenez, JT Rabban. UCSF, San Francisco, CA

Background: Peritoneal carcinomatosis due to primary peritoneal cancer or metastasis often presents with radiologic omental caking. Morphologically, tumor cells typically infiltrate omental or peritoneal tissues in a destructive pattern. Some forms of cancer, such as gastric or breast cancer can spread with minimal destruction. This study reports an unusual variant of peritoneal carcinomatosis due to metastatic gastric or breast cancer in which sparse tumor cells line the peritoneal/omental surface/septae with minimal or no stromal invasion yet diffuse fibrosis is present. We report the pathologic features and diagnostic pitfalls of this variant pattern, which we term "omental icing".
Design: Peritoneal carcinomatosis cases due to gastric(36) or breast cancer(7) were evaluated. Tumor growth pattern was classified as: Pattern A= destructive invasion of fat or mass-like growth; Pattern B= non-destructive/infiltrating tumor cells confined to a thin layer at the peritoneal surface; Pattern C= Pattern B with sparse tumor cells along omental fat septae or minimal hypocellular infiltrate of fat. Omental fibrosis, atypical fibroblasts and stromal inflammation were graded. Tumor nuclear grade, signet ring morphology, LVI and mitosis were evaluated.
Results: Primary gastric/breast cancer was known prior to surgery in 34/43 cases; primary peritoneal origin was suspected in 9/43. Omental caking was seen radiologically in 14/38 and 14 had elevated serum CA125. Tumor morphology was: pattern A: 19 ;pattern B: 1;pattern C: 23. Among the 24 pattern B/C tumors: frozen sections were definitive in 21/24. In permanent sections tumor cells were visible only on high magnification and often obscured by fibrosis/inflammation. Tumor cells were purely single cells in 17/24; clusters/tubules in 2/24 or a mixed in 5/24. Signet rings were in 14/24. Nuclear atypia was mild (7), moderate (15) or severe (1). Mitoses were absent or sparse (avg 1.5/10 hpf). Despite sparse tumor cells, extensive diffuse omental fibrosis and inflammation was present in 15/24. Atypical stromal fibroblasts were in 3/24.
Conclusions: Peritoneal carcinomatosis from gastric or breast cancer may present with significant omental caking due to diffuse stromal fibrosis despite sparse tumor cells confined to the omental surface or septae. This so-called omental icing pattern may pose diagnostic challenges, particularly at frozen section since tumor cells often show only low grade atypia, scant mitoses and lack signet rings. Attention to omental surface and septae can prevent under-recognition of this unusual pattern of tumor growth.
Category: Gynecologic & Obstetrics

Wednesday, March 24, 2010 1:00 PM

Poster Session VI # 174, Wednesday Afternoon


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