Cancer of the ampulla of Vater: chromosome 17p allelic loss is associated with poor prognosis

Abstract

Background: Cancer of the ampulla of Vater kills 60% of affected patients. Local spread of the tumour (T stage) is the only reliable prognostic factor. Nevertheless, any cancer stage includes long term survivors and patients dying from the disease. The molecular anomalies involved in this process have the potential to serve as additional prognostic markers.

Aim: To evaluate if allelic losses (LOH) of chromosomes 17p and 18q may be of prognostic value in multivariate survival analysis.

Methods: We examined 53 ampullary cancers for chromosome 17p and 18q LOH using microsatellite markers and DNA from paraffin embedded tumours. All patients were treated by surgery alone (pancreaticoduodenectomy). Multivariate survival analysis included age, sex, tumour size, macroscopic appearance, grade of differentiation, T stage, lymph node metastasis, and chromosome 17p and 18q status.

Results: Chromosome 17p and 18q LOH were detected in 28 (53%) and 18 (34%) cancers, respectively. Multivariate survival analysis indicated chromosome 17p status as an independent prognostic factor together with T stage. The five year survival for chromosome 17p retention and 17p loss was 80% and 7%, respectively. The risk of death from cancer within the five year follow up period for patients with cancers harbouring chromosome 17p LOH was 11 times higher than that of patients with cancers retaining chromosome 17p (p<0.0001), regardless of the tumour stage at diagnosis.

Conclusions: Chromosome 17p status is an independent prognostic factor among ampullary cancers at the same stage. The combined use of T stage and chromosome 17p status may help in deciding whether ampullary cancer patients require additional therapy other than surgery alone.

Figure 1

(A) Analysis of polymerase chain reaction (PCR) amplified microsatellite locus D17S559, localised at chromosome 17p13, using high molecular weight DNA from frozen tissues. Case numbers are indicated at the top of each lane and correspond to those of table 1. T, tumour; N, matched normal tissue DNA. The upper allele is lost in cancers 1, 3, 14, and 20 whereas loss of the lower allele is evident in cancers 2, 5, and 15. Case Nos 4, 27, 9, 26, 17, 18, 19, and 22 show no losses. Case Nos 8, 11, 12, 16, 21, 23, and 24 were considered as non-informative. Cancers 7 and 25 are good examples of the possible findings in replication error (RER) positive neoplasms, showing the disappearance of one allele with the appearance of a new one, the presence of additional longer or shorter fragments, or a combination of these phenomena. Case Nos 9, 11, and 21 are three adenomas, two of which have been described previously.^9 11 (B) Analysis of PCR amplified microsatellite loci of chromosome 18q, using DNA from formalin fixed, paraffin embedded tissues. Microsatellite loci are indicated at the bottom of each panel. Allelic losses occurred in cancers 1, 3, 19, 20, 27, 12, and 2. Case No 15 is an example of allelic imbalance due to the increased intensity of one allele in the absence of a decrease in intensity of the other. This case was considered as not having allelic loss as such a pattern may well be attributable to partial or total chromosomal gains (for example trisomies). Case No 11 is a previously described adenoma.⁹

Figure 2

Survival curves obtained by the product-limit method. Better survival was associated with no loss of chromosome 17p (p<0.0001) or 18q (p<0.0001) (A, B) and T stages II-III compared with stage IV (p<0.0001) (C). (D) Overall survival of patients according to both T stage and chromosome 17p status. Numbers in parentheses indicate the number of subjects at risk at different time intervals. Vertical lines indicate 95% confidence intervals.

Figure 3

Molecular pathogenesis and prognosis of cancers of the ampulla of Vater. Ampulla of Vater cancers have similar molecular pathogenetic pathways as gastric and colorectal cancers. The majority of cases (85%) show frequent chromosomal changes (CIN, chromosomal instability), while a subgroup (15%) shows subtle widespread DNA alterations (MIN, microsatellite instability). In CIN type ampullary cancers, the early genetic events include mutation of the adenomatous polyposis coli (APC) and Ki-ras genes in 17% and 37% of cases, respectively, together with chromosome 5q loss (50%).^9-12 Mutation of the p53 gene occurs in about 50% of cases at the time of adenoma-carcinoma transition.^6 9 11 Allelic losses at chromosomes 17p (51%) and 18q (33%) are associated with progression of malignancy. MIN type ampullary cancers rarely show chromosomal losses. The two molecular pathways identify different prognostic categories. MIN ampullary cancers have a low aggressive potential,⁶ similar to that of CIN cancers, retaining both copies of chromosome 17p. Chromosome 17p loss is associated with a high risk of death from cancer within two years following surgery.