Association of allelic imbalance at locus D13S171 (BRCA2) and p53 alterations with tumor kinetics and chromosomal instability (aneuploidy) in nonsmall cell lung carcinoma.
BACKGROUND
BRCA2 gene, located at chromosome 13q12.3, frequently is altered in familial types of cancer in which a "double-hit" inactivation model seems to occur. In contrast, in sporadic forms of cancer there is frequent absence of a second event (point mutations) suggesting that allelic imbalance at the BRCA2 locus may be associated with a "gene dosage effect" of BRCA2 function. Little is known about BRCA2 allelic alterations in nonsmall cell lung carcinomas (NSCLCs). Furthermore, recent studies suggest that BRCA2 and p53 participate in a common pathway involved in DNA damage repair. In view of this putative link, the authors investigated in a series of 63 NSCLCs: 1) the allelic imbalance (AIm) at the D13S171 (BRCA2) locus, 2) the possible relation with tumor kinetics (proliferation [PI] and apoptotic indices [AI]) and chromosomal instability (aneuploidy) of the carcinomas, and 3) the mutual impact of D13S171 AIm and p53 altered status on the above-mentioned parameters.


METHODS
Allelic status of the BRCA2 region was examined in a series of 63 NSCLCs, by using the polymorphic marker D13S171, which is located in the center of it. Most information regarding the status of p53 at the immunohistochemical and genetic levels was obtained from a previous analysis. Tumor kinetic parameters (proliferation and apoptotic indices) were determined using Ki-67 immunohistochemical analysis and Tdt-mediated dUTP nick end labeling assay, respectively. Chromosomal instability (aneuploidy) was assessed by measuring nuclear DNA ploidy with an image analysis system.


RESULTS
Allelic imbalance at D13S171(BRCA2) was observed in 70% of the informative cases (H: heterozygous) with a rather high frequency of occurrence (50%) in Stage I disease, suggesting a possible early involvement in the development of NSCLCs. Although no association was found among loss of heterozygosity (LOH) at D13S171, kinetic parameters and ploidy status of the tumors and concurrent alterations in BRCA2 and p53 (BRCA2[LOH]/p53[P]), which was the most frequent profile (37.2%), had the highest growth index (PI/AI mean value ratio) that differed significantly only from the BRCA2(LOH)/p53(N) pattern (P = 0.027). This difference was attributed to the high AI of the BRCA2(LOH)/p53(N) pattern (P < 0.001), whereas PI was similar among all BRCA2/p53 profiles. Also the "full abnormal pattern" was associated with aneuploidy, whereas the BRCA2(LOH)/p53(N) profile was mainly diploid. When these indicators and conventional prognostic ones were examined for effect on patient survival, only stage and lymph node status showed a significant correlation, whereas LOH at D13S171 (BRCA2), p53 abnormalities, proliferative and apoptotic indices, ploidy status, smoking history, and histology and combinations of LOH and p53 abnormalities failed to show significant correlation with survival.


CONCLUSIONS
These findings suggest that in BRCA2(LOH) NSCLCs the status of p53 (wild type or mutant) represents a decisive determinant of tumor growth and chromosomal instability. Nevertheless, a possible synergistic effect from loss of D13S171 region with p53 abnormalities cannot be excluded because the BRCA2(LOH)/p53(P) profile compared with the BRCA2(H)/p53(P) one had a higher PI/AI mean value ratio (31.05 vs. 22.97), although it was not statistically significant. However, we cannot exclude the possibility that LOH at D13S171 reflects deletion of other putative tumor suppressor gene(s) in the proximity of BRCA2. In this respect, more studies are needed to understand the involvement of BRCA2 region alterations in nonsmall cell lung carcinogenesis. (c) 2000 American Cancer Society.
Gorgoulis
V G
VG
Department of Histology and Embryology, Medical School, University of Athens, Greece.
Kotsinas
A
A
Zacharatos
P
P
Mariatos
G
G
Liloglou
T
T
Tsoli
E
E
Kokotas
S
S
Fassoulas
C
C
Field
J K
JK
Kittas
C
C
D000782:Aneuploidy; D017209:Apoptosis; D024682:BRCA2 Protein; D002289:Carcinoma, Non-Small-Cell Lung / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002455:Cell Division; D004273:DNA, Neoplasm / Q000032:analysis; D016158:Genes, p53; D006801:Humans; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008175:Lung Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D018895:Microsatellite Repeats; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics*; D011379:Prognosis; D016019:Survival Analysis; D014157:Transcription Factors / Q000235:genetics*
D024682:BRCA2 Protein; D004273:DNA, Neoplasm; D009363:Neoplasm Proteins; D014157:Transcription Factors