In this study, we demonstrated a higher recurrence rate in patients curatively operated for CRC stages I–III with moderate or high intensity of GDF15 expression, compared with tumours with no or low intensity of GDF15 expression. This was also demonstrated separately for patients with stage III disease, but not for patients with stage II disease.
Our data are consistent with previous findings by Xue et al (2010)
who investigated the expression of GDF15 in 69 CRC cases by immunohistochemistry. They demonstrated not only an association between upregulation of GDF15 and development of metastases but also, different from our study, an increased immunohistochemical GDF15 expression in stages III and IV compared with stages I and II. However, unlike our study, the study by Xue et al (2010)
used a combined score to quantify the intensity and fraction of GDF15 immunostaining, thus, limiting further comparisons between the two studies.
Brown et al (2003)
demonstrated an association between high GDF15 blood levels, presence of metastatic disease and an elevated risk of death. In our study, we observed that the risk of death was more than two times higher (HR 2.2; 95% CI, 1.3–3.7) in patients with elevated GDF15 plasma levels (>116
p per 5μ
l), which can be compared with the results documented on patients with elevated GDF15 serum levels (>1150
) by Brown et al (2003)
(OR 2.11; 95% CI, 1.04–4.28). In our study, the plasma levels of GDF15 were not significantly different between patients with or without recurrence in stages I–III, even though there was a trend of a higher plasma levels in patients with recurrence in stage III.
The presence of vascular invasion is known to be an independent prognostic factor for both colon (Shepherd et al, 1989
; Petersen et al, 2002
) and rectal cancer (Talbot et al, 1980
; Willett et al, 1999
; Smith et al, 2008
). A study by Petersen et al (2002)
even proposed that the presence of vascular invasion along with three other pathologically determined parameters could be used to make decisions regarding adjuvant therapy in stage II CRC. In our study, increased GDF15 expression was negatively associated with vascular invasion. This observation is supported by a previous report on the anti-angiogenic activity of GDF15 (Ferrari et al, 2005
) in which GDF15 was demonstrated both in vivo
and in vitro
to inhibit angiogenesis in endothelial cells. This inconsistent finding, of decreased vascular invasion and higher risk for recurrences, could be a result of the increased likelihood of a significant outcome by chance because of multiple testing; nevertheless, it could also be explained by the divergent molecular mechanisms of GDF15. GDF15 has been implicated both as a promoter and inhibitor of tumour growth (Tan et al, 2000
; Baek et al, 2001
; Levy and Hill, 2006
; Abd El-Aziz et al, 2007
; Johnen et al, 2007
). The conflicting results between in vitro
and in vivo
studies regarding the role of GDF15 in tumourigenesis can probably be attributed to the interaction of the tumour with the microenvironment (Albertoni et al, 2002
; Krieg et al, 2010
). The current belief is that GDF15 has pleiotropic effects in cancer progression by functioning as a tumour suppressor inhibiting tumour growth, inducing apoptosis in early stages, although it promotes proliferation, migration, invasion and metastasis in more advanced disease stages (Mimeault and Batra, 2010
). This belief of a dual and stage-dependent role of GDF15 in tumourigenesis could potentially, in our study, explain why a high intensity of GDF15 expression was associated with a shorter time to recurrence in stage III but not in stage II disease.
We confirmed a difference in the intensity of immunoreactivity of GDF15 between normal mucosa and invasive tumour tissue, but failed to demonstrate a difference in the fraction of GDF15-positive cells between normal tissue and invasive tumour tissue. This indicates that there might be a pathophysiological distinction between activity of GDF15 expression (measured as intensity) and actual number of cells expressing GDF15 (measured as fraction) between invasive tumour tissue and normal mucosa, supporting that intensity of immunoreactivity rather than fraction of positive cells for GDF15 better serves as a prognostic marker in CRC.
Plasma levels of GDF15 have been studied as a biomarker in cardiovascular disease (Hochholzer et al, 2010
) and elevated levels have been seen in metastatic CRC, breast and prostate carcinomas compared with normal controls (Welsh et al, 2003
). The correlation between GDF15 plasma levels and CEA in the whole cohort including all disease stages was weak, but when analysing patients with stage IV disease, a stronger correlation was observed. We demonstrated a gradual trend of increasing GDF15 plasma levels from stage I to IV, whereas the CEA levels were low in patients with early disease stages, but significantly elevated in stage IV patients. The predictive value of CEA for detecting colorectal cancer in early stages is known to be low (Fletcher, 1986
), although there is clear evidence that preoperative plasma CEA levels correlate with stage and serve as an independent prognostic factor of survival (Wanebo et al, 1978
; Wolmark et al, 1984
; Slentz et al, 1994
). Consistent with a previous study by Brown et al (2003)
, GDF15 plasma levels in our study was an independent prognostic factor of survival supporting that measurement of GDF15 levels in plasma might add additional prognostic information in patients with CRC. The samples in our study were strategically selected to get a more reliable estimate the GDF15 plasma analyses but still limited by the small sample size and, therefore, decreased the power and the precision of the results.
Other issues regarding immunohistochemistry related to different fixation techniques and duration of fixation of the tumour tissue could potentially also have influence our results (Atkins et al, 2004
; Leong, 2004
; Paavilainen et al, 2010
). However, in our study all tissue specimens were handled at the same pathology department. Consequently, in this prospectively collected material, we predict low variability of the actual handling of the tissue specimens. The antibody used in the immunohistochemistry staining had a high specificity on protein array and a single band corresponding to the predicted size in kDa on the western blot. Therefore, we believe that it is less likely that the specificity of the antibody influenced our results.
In conclusion, we have demonstrated that increased GDF15 expression may have a negative prognostic value in patients curatively operated for CRC stages I–III and III disease. However, the actual role of GDF15 in tumourigenesis is still unclear, and further research regarding both its pathophysiological role and clinical use as a prognostic marker for CRC is needed preferably in prospective clinical trials.