[773] Low-Grade Appendiceal Mucinous Neoplasms Show Activation of the Mitogen Activated Protein (MAP) Kinase Pathway

Rhonda K Yantiss, David B Solit, Manickam Janakiraman, Joseph Misdraji. Weill Cornell Medical College, New York, NY; Memorial Sloan Kettering Cancer Center, New York, NY; Massachusetts General Hospital, Boston, MA

Background: Low-grade appendiceal mucinous neoplasms are classified as mucinous cystadenomas (MCAD) when confined to the appendiceal muscularis mucosae and well-differentiated mucinous adenocarcinomas (MACA) when they invade the appendiceal wall or spread to the peritoneum (pseudomyxoma peritonei). The molecular features of these uncommon tumors have not been extensively studied. We evaluated 86 cases, including 60 MCADs and 26 MACAs, for mutations affecting RAS/RAF/MEK/ERK signaling.
Design: DNA was extracted from 60 MCADs and paired samples of appendiceal and peritoneal tumors from 26 patients with MACAs using a 96-well plate format. Template DNA (10-20 ng) and PCR master mixes were dispensed into 384 well plates for PCR cycling. Subsequent primer extension products were analyzed using the Sequenom platform, which is more sensitive than direct sequencing and amenable to multiplex assessment of multiple candidate mutations. Amplified products were dispensed onto the Sequenom Spectro-chip and assessed for KRAS, BRAF, PIK3CA, AKT1, and NRAS mutations using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS).
Results: Oncogenic KRAS point mutations were detected in 31 (52%) MCADs involving codons 12 (n=29) and 13 (n=2). Three (5%) MCADs contained hotspot mutations in PIK3CA (1 E542 and 2 E545 mutations). Eighteen (69%) MACAs had KRAS mutations affecting codons 12 (n=16) and 13 (n=2) that were identical in appendiceal and peritoneal components in 9 cases. Five MACAs showed mutations in the appendiceal tumor, but not the peritoneum, reflecting the paucicellular nature of peritoneal disease. Four others had new mutations in the peritoneal tumor compared to the appendix. Three (12%) MACAs showed activating PIK3CA mutations limited to peritoneal deposits (1 E542K and 2 M1043I mutations). All appendiceal mucinous neoplasms were BRAF, AKT, and NRAS wild-type.
Conclusions: A high proportion (58%) of low-grade appendiceal mucinous neoplasms harbor activating KRAS mutations. These changes are present even when the tumor is a mucinous cystadenoma confined to the appendix. Activating PIK3CA mutations are infrequent (7%), but may be more common in advanced tumors. Mutations affecting BRAF, AKT, and NRAS do not play a major role in appendiceal mucinous neoplasia. These findings may be important to developing treatment strategies in the future.
Category: Gastrointestinal

Monday, March 19, 2012 1:00 PM

Poster Session II # 112, Monday Afternoon


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