Most patients with gastric cancer are unresectable at diagnosis, or will suffer a relapse after surgery, resulting in a five year overall survival of less than 20%.39–41
Preoperative chemotherapy could be an approach that might improve surgical resectability, which is one of the main prognostic factors in patients with gastric carcinoma.42
However, only 40–50% of patients benefit from this treatment modality, whereas approximately 30% of patients experience moderate to severe toxic side effects.6,8,43
Understanding the molecular genetic features that determine response or resistance to chemotherapy could permit the selection of the most suitable patients for preoperative treatment.
“Histological responders underwent surgical treatment in all cases and survived significantly longer than non-responders”
To test the hypothesis that dose escalation would provide a benefit with regard to resectability and overall survival, a phase II study was designed to determine the feasibility of etoposide, cisplatin, and mitomycin based HDCT followed by ABMT in a preoperative setting. In our study, we evaluate clinical, histological, and molecular markers and their associations with response to treatment and survival in this highly selected patient cohort.
Patients who underwent resection survived significantly longer than unresected patients. These data demonstrate that resectability after preoperative chemotherapy is prognostically beneficial for patients with advanced gastric cancer. However, the benefit of post-chemotherapeutic surgical treatment on the overall survival of the entire patient cohort could not be shown unequivocally, because only the patients with a clinical response underwent gastrectomy in our study.
Interestingly, the histological examination of gastrectomy specimens and biopsies obtained after chemotherapy could predict overall survival of the patients. Histological responders underwent surgical treatment in all cases and survived significantly longer than non-responders. This is in accordance with previous studies, which reported a trend towards decreased survival in patients with a poor histological response.44,45
However, it has to be considered that a detailed histopathological evaluation of histological regression of gastric cancer using several paraffin wax blocks of gastrectomy specimens is not entirely comparable to the findings investigating biopsies of patients with non-resectable cancer. To minimise the bias in this comparison, five biopsies with at least 18 sections for each biopsy were analysed.
The molecular markers analysed in this study included MSI, LOH at the p53 and APC loci, expression and mutation of the p53 tumour suppressor gene, and expression of the proapoptotic protein BAX.
Overexpression of p53 and the presence of p53 mutations in exons 5–9 in pretreatment biopsy specimens were significantly associated with increased overall survival. In addition, p53 protein expression and mutation status were the only clinical or molecular parameters associated with objective tumour regression and histological response.
Given the important role of wild-type p53 in apoptosis and the association of p53 mutations with poor survival in many tumour types,46
these results were surprising. In contrast to our results, p53 expression detected by immunohistochemistry in pretreatment endoscopic biopsies was associated with poor response to neoadjuvant cisplatin based chemotherapy in patients with gastric cancer in two studies.47,48
In a study by Kubicka et al
positive lymph nodes and p53 mutations were the only significant adverse prognostic markers for survival after curative resection for gastric cancer. However, there are also reports in which p53 overexpression and/or mutation is associated with better outcome after treatment of bladder cancer or glioblastoma.50,51
In our study, seven of the responding tumours, but only one of the non-responding tumours, showed mutations in exons 5–9 of the p53 gene. In addition, p53 LOH was found in the gastric cancers of eight of the responders and three of the non-responders. Two of the responders had both p53 mutation and p53 LOH. Fifty per cent of gastric cancers contain p53 mutations, and p53 LOH has been reported in 26–83% of cases.52
Sano et al
found both LOH and p53 mutations in more than 60% of gastric tumours.53
In contrast, Kobayashi et al
demonstrated cases of gastric cancer that displayed LOH and did not contain p53 mutations, and vice versa,54
which is similar to our findings. Ikeguchi et al
described cisplatin induced apoptosis more frequently in gastric cancer cell lines with a wild-type p53 gene.55
In contrast, Grundei et al
found that LOH at the p53 locus in advanced gastric cancer is associated with a good clinical response to cisplatin based neoadjuvant chemotherapy.56
A possible explanation is that p53 overexpression does not correlate with the inactivation status of the gene,57,58
or that we may have detected overexpression of the wild-type protein59
in a subset of patients. This could indicate an accelerated response to stress factors (such as DNA damage induced by cisplatin60
), with subsequent effective tumour cell elimination by apoptosis. However, the association between p53 expression and mutational status on the one hand and between p53 mutations and prolonged overall survival on the other hand argues against this hypothesis.
p53 is known to be an important determinant of DNA damage induced apoptosis, and loss of p53 in tumours is associated with an unfavourable prognosis in many forms of cancer.61–63
Wild-type p53 is thought to render tumours more sensitive to treatment by the induction of apoptosis, and p53 inactivation may lead to resistance to treatment. However, because p53 is also responsible for prolonged cell cycle arrest after chemotherapy induced genetic damage, it is expected to facilitate DNA repair in the absence of an apoptotic response. Therefore, tumours that inactivate p53 during progression should be less capable of DNA repair and more sensitive to a DNA damage induced mitotic catastrophe. Specific mutant forms of p53 also confer a gain of function phenotype, manifested by augmented cell growth and tumorigenic potential. Blandino et al
found that mutations at p53His175 and p53His179 provided substantial resistance to etoposide, whereas the protective effect of p53His273 and p53Trp248 was much milder.64
Mutant p53 can inhibit apoptosis after treatment of cancer cells with low drug concentrations (for example, cisplatin), but had no effect after the presence of high concentrations. These findings suggest a possible selective gain of function of mutant p53 that depends on the particular mutation and the identity and concentration of the chemotherapeutic drug. In summary, loss of p53, and possibly gain of function of the mutant p53 protein, might not lead to increased resistance of tumours to treatment, but could be a factor that contributes to sensitivity to chemotherapy.65
Microsatellite analyses revealed that none of the patients with advanced gastric cancers showed an MSI-H genotype. This is in agreement with the better prognosis of MSI positive gastric cancer,66
leading to an under-representation of MSI positive tumours in this highly selected patient cohort with advanced tumours.
“p53 protein expression and mutation status were the only clinical or molecular parameters associated with objective tumour regression and histological response”
Preoperative chemotherapy can increase the rate of curative resection in locally advanced gastric carcinoma. However, a significant response or survival advantage is only seen in less than half of patients treated.67
The only prognostic factors that are commonly accepted in gastric cancer are clinicopathological features, such as performance status, patient age, or macroscopic tumour type.68,69
The examination of molecular alterations on pretreatment biopsy samples may be of particular importance for identifying those patients who would be suitable for preoperative chemotherapy, in an attempt to achieve resectability, the main prognostic factor for survival in gastric cancer. Without appropriate predictive markers, patient selection is based on clinical staging parameters and results in the treatment of more than twice as many patients than will eventually benefit from such treatment.
Take home messages
- Positive p53 immunostaining, positive p53 mutation status before chemotherapy, strong histological regression induced by preoperative high dose chemotherapy (HDCT), and surgical treatment were significantly associated with response to chemotherapy and prolonged overall survival
- Thus, positive p53 immunostaining and p53 mutation status in pretreatment tumour biopsies might be useful molecular predictors of response and prognosis in patients with advanced gastric cancer treated by preoperative HDCT
- Clinical or biological markers that could predict reponse to such treatment would be extremely useful
- Prospective follow up evaluation and investigation of additional molecular markers are warranted to define effective predictors for response to chemotherapy in patients with gastric cancer
The results of our study indicate that overexpression and mutation of p53 in pretreatment biopsy specimens could predict overall survival in patients with advanced gastric cancer receiving preoperative HDCT. The availability of clinical or biological markers to predict response to such treatment would be highly desirable. Prospective follow up evaluation and investigation of additional molecular markers are warranted to define effective predictors for response to chemotherapy in patients with gastric cancer.