Thomas, N.; Alexander, A.; Edmiston, S.; Millikan, R.; Groben, P.; Hao, H.; Tolbert, D.; Berwick, M.; Busam, K.; Begg, C.; Hummer, A.; Mattingly, D.; Ollila, D.; Conway, K. Author Information

10048 Background: LCCC9819 and I-SPY1 are designed to examine multiple potential predictive markers and assays simultaneously in biopsies from neoadjuvantly treated patients. Both p53 mutation status and molecular ‘intrinsic‘ subtype have been associated with chemosensitivity. In this preliminary analysis, we present the p53 mutation spectra by molecular subtype from patients enrolled in the combined LCCC 9819 and I-SPY1 datasets. Methods: Patients received neoadjuvant anthracycline-based chemotherapy with pre-therapy biopsies. p53 mutation analysis was performed by p53 GeneChip assay for point mutations/1 bp deletions followed by SSCP if GeneChip-negative. Abnormal GeneChip or SSCP were confirmed by sequencing. DNA microarrays used Agilent human microarrays and a common reference strategy approach. Results: 51 patients were treated on LCCC9819 and have available molecular analyses; 87 from I-SPY1. 111 patients have completed p53 mutation analysis, revealing a high proportion (42%) with abnormal p53. Of these, several were in known hotspots, including R175H (4 mutations), R248L (1), R273H (3), and R273C (2). Most were missense mutations (81%), however, there were 8 (17%) null and 1 (2%) silent mutations. Most (91%) mutations were in the DNA binding domain. Molecular subtypes are known on 111 tumors: 22% Luminal A, 22% Luminal B, 3% Normal-like, 23% HER2+/ER−, 27% Basal-like, and 3% unclassified. Among those with both assays complete, we found that p53 mutations differed by subtype (Table). Conclusions: P53 mutations are common in these independent neoadjuvant datasets, and differ in frequency between molecular subtypes, which may have implications for predictive factor identification. Future analyses will include aCGH, cell cycle protein analysis, proteomics, and clinical data including response to chemotherapy. (supported by UNC Breast SPORE-CA58223, NIH M01RR00046, DAMD 17–02–1-0521). [Table: see text] No significant financial relationships to disclose.

Recent studies have shown the p19(ARF) tumor suppressor to be involved in the response to oncogenic stress by regulating the activity of p53. This response is mediated by antagonizing the function of Mdm2, a negative regulator of p53, indicating a pathway for tumor suppression that involves numerous genes altered in human tumors. We previously described a transgenic mouse brain tumor model in which oncogenic stress, provided by cell-specific inactivation of the pRb pathway, triggers a p53-dependent apoptotic response. This response suppresses the growth of developing tumors and thus represents a bona fide in vivo tumor suppressor activity. We further showed that EM, a transcription factor known to induce P19(ARF) expression, was required for the response. Here, we use a genetic approach to test whether p19(ARF) functions to transduce the signal from E2F1 to p53 in this tumor suppression pathway. Contrary to the currently accepted hypothesis, we show that a deficiency in P19(ARF) has no impact on p53-mediated apoptosis or tumor suppression in this system. All measures of p53 function, including the level of apoptosis induced by pRb inactivation, the expression of p21. (a p53-responsive gene), and the rate of tumor growth, were comparable in mice with and without a functional p19(ARF) gene. Thus, although p19(ARF) is required in some cell types to transmit an oncogenic response signal to p53, it is dispensable for this function in an in vivo epithelial system. These results underscore the complexity of p53 tumor suppression and further indicate the existence of distinct cell-specific pathways that respond to similar stimuli.

BACKGROUND & AIMS:Our long-term goal was to evaluate the role of p53 in the prognosis of gastric cancer. We previously showed a discrepancy between p53 expression and the presence of mutations when only exons 5-9 were examined. We then evaluated exon 4.METHODS:DNA was sequenced from 217 gastric cancers to detect exon 4 alterations. Codon 72 was examined by restriction enzyme digestion.RESULTS:Mutations were present in 3.2% of tumors. In addition, 2 polymorphic sites were found at codons 36 and 72. Polymorphisms at codon 36 were only found in 2 patients. In contrast, the codon 72 polymorphism was very frequent. The genotype frequency was arg/arg (54%), arg/pro (33%), and pro/pro (14%). The genotype of the polymorphic site varied with race (P = 0.001): 64% of whites had the arg/arg genotype, compared with 24% of blacks. The difference in genotype by site, sex, or histological tumor type was not statistically significant (P = 0.067).CONCLUSIONS:There are several exon 4 alterations in gastric cancers. These include the rare mutations and the very rare codon 36 polymorphism. The most common change is the codon 72 polymorphism, the genotype of which differs significantly with race. The more common arg/arg genotype in whites may explain why whites are more prone to develop cardiac cancer, whereas the more common proline allele in blacks may explain why they are more prone to develop antral cancers. Further studies are required to determine whether the codon 72 polymorphism affects patient predisposition to gastric cancer.

Objectives: We investigated p53 gene mutations in advanced gastric cancers by direct DNA sequencing, in order to determine the frequency of mutations in gastric cancers having different epidemiological backgrounds, tumors of the cardia were compared with those arising in the antrum or corpus. Intestinal type cancers were compared with diffuse or other histologic types. We have chosen to assess the frequency of mutations solely based on DNA sequencing.