The ampulla’s pathologic and clinical significance is out of proportion to its small size. Tumors arising at this location have the potential to obstruct 2 major organs often resulting in early detection and presumably contributes to better prognosis when compared with carcinomas of adjacent structures, particularly the pancreas.19
However, studies comparing stage-matched ampullary and pancreatic adenocarcinomas still maintain more favorable outcome for AACs,13,53
suggesting a biology difference.
Nevertheless, the large variance in AAC survival rates (reported 5-year survival varying from 21% to 68%),19
owing partly to the improper characterization of true AACs in the literature, is striking. Oncologists have been searching for pathologic indicators that predict clinical outcome more accurately and striving to develop appropriate management algorithms. So far, the factors most consistently reported to influence prognosis have been grade and stage.1
In their study of the SEER (Surveillance Epidemiology End Results) database, Al-bores-Saavedra et al showed that (1) overall survival of AAC is directly related to histologic grade and high-grade tumors tend to show more aggressive behavior than lower-grade tumors and tend to present at deeper levels of mural infiltration with more nodal involvement and more likely metastatic spread (2) stage of the disease is the most important prognostic factor for survival. Patients with localized-stage disease have significantly more favorable 5-year survival rate (45%) than patients with regional (31%) or distant-stage disease (4%). Their findings are consistent with data from smaller series.5,21,25,26,29,36,54
Other studies have reported a significant association of lymphovascular invasion,11,26,29,53,54
and margin status2
with patient survival. Although there is not much datum in the literature, MIB-1 index,45
and microsatellite instability39
have also been proposed as prognostically relevant factors. Some even suggest that MIB-1 index and DNA ploidy are independent prognostic parameters with an impact on survival higher than the grade and stage.44,45
Although recently a more favorable survival rate for intestinal-type relative to pancreatobiliary-type AACs has been shown,1,5,8,38,55
it is unclear if this difference is independent of stage. In our study, intestinal-type AACs was found to have a significantly better prognosis than nonintestinal-type AACs (P
Tumor budding shows increasing promise in clinicopathologic studies as a prognostic factor independent of stage, in colorectal carcinomas28,31,33,51
and in esophageal20,24,37
and anal squamous cell carcinomas30
; however, it had not been studied in AACs.
The mechanism of budding has not yet been fully clarified, but it is thought to occur as a feature of the dedifferentiation observed at the invasive margin, and to represent the initial phase of tumor invasion.51
Studies indicate that epithelial-mesenchymal transition has an important role in the process.32
In the early phase of epithelial-mesenchymal transition, tumor cells undergo reduced intercellular contacts mediated by e-cadherin and start cell-matrix contacts mediated by integrins leading to reorganization of actin cytoskeleton to form cytoplasmic protrusions. When new cell-matrix contacts are completed at the leading edge, migration follows. Recently, loss of the E-cadherin/beta-catenin complex was shown to be related to poor prognosis in ampullary cancer.14
Furthermore, matrix metalloproteinases and the urokinase plasminogen activator (uPA)/uPA receptor system initiate pericellular matrix degradation.3,4
Not surprisingly, studies that address tumor budding have also shown altered cohesiveness of budding cells and degradation of the extracellular matrix.9,12,23,32,34,35,43
In this study, the prevalence, and possible prognostic significance of budding was analyzed in a large series of AAC. Cases were identified based on stringent criteria, which excluded tumors that secondarily invade the ampulla, whereas most surgical databases commonly included these as “ampullary” cancer cases (see materials and methods). Hence, this study of 244 cases is by far the largest pathologically characterized series of AACs. In analyzing the budding in this series, a modified version of the method put forth by Ueno et al51
was used. The entire invasive tumor front was carefully evaluated given the observation of heterogeneous nature of tumor budding. Variance in the amount and degree of budding was noticed and categorized into 2 groups: AACs in which tumor budding was easily observed with patchy or diffuse distribution (high-budding) and those with minimal or no budding (low-budding). For this, we defined greater than or equal to 5 isolated single cancer cells or clusters composed of fewer than 5 cancer cells per 20 × (0.785 mm2
) as budding focus (), and the presence of greater than equal to 3 such foci as high-budding.
This study shows high-budding in AAC is strongly associated with larger invasion size, infiltrative growth pattern, worse differentiation, higher incidence of lymphatic and perineural invasion and lymph node metastasis, which suggests that tumor budding contributes to invasiveness, spread of AACs, and may be one of the key factors in lymph node metastasis. This may not be surprising, considering the biological significance of budding discovered recently in other organ systems. Most importantly, high-budding is an independent prognostic parameter with an impact (HR: 2.64) even greater than established outcome predictors such as T-stage and N-stage. In addition, when a restricted subset of the study population were analyzed independently, budding still served as a stratifying factor for both lower stage and well-differentiated categories, and cases with expansive growth.
In conclusion, tumor budding is frequently encountered in AAC. High-budding is a strong independent predictor of overall survival, with a prognostic correlation stronger than the established parameters of tumor stage and lymph node metastasis. Therefore, tumor budding should be incorporated into surgical pathology reports for AAC.