Desmoplasia in Primary Tumors and Metastatic Lesions of Pancreatic Cancer

Abstract

Purpose: Pancreatic ductal adenocarcinoma (PDAC) is characterized by high levels of fibrosis, termed desmoplasia, which is thought to hamper the efficacy of therapeutics treating PDAC. Our primary focus was to evaluate differences in the extent of desmoplasia in primary tumors and metastatic lesions. As metastatic burden is a primary cause for mortality in PDAC, the extent of desmoplasia in metastases may help to determine whether desmoplasia targeting therapeutics will benefit patients with late-stage, metastatic disease.

Experimental design: We sought to assess desmoplasia in metastatic lesions of PDAC and compare it with that of primary tumors. Fifty-three patients' primaries and 57 patients' metastases were stained using IHC staining techniques.

Results: We observed a significant negative correlation between patient survival and extracellular matrix deposition in primary tumors. Kaplan-Meier curves for collagen I showed median survival of 14.6 months in low collagen patients, and 6.4 months in high-level patients (log rank, P < 0.05). Low-level hyaluronan patients displayed median survival times of 24.3 months as compared with 9.3 months in high-level patients (log rank, P < 0.05). Our analysis also indicated that extracellular matrix components, such as collagen and hyaluronan, are found in high levels in both primary tumors and metastatic lesions. The difference in the level of desmoplasia between primary tumors and metastatic lesions was not statistically significant.

Conclusions: Our results suggest that both primary tumors and metastases of PDAC have highly fibrotic stroma. Thus, stromal targeting agents have the potential to benefit PDAC patients, even those with metastatic disease.

Figure 1

Kaplan-Meier survival curves for patients with high and low levels of hyaluronan (HA) and Collagen I (Col I) in their primary tumors. Average staining positivity for HA in patient tissues was plotted in Kaplan-Meier curves which allowed us to compare ‘low’ and ‘high’ HA level groups. Median survival in the ‘high’ HA group was 9.3 months, as opposed to 24.3 months for the ‘low’ HA group. This difference amounted to a separation of 15.0 months in median survival between the ‘low’ HA and ‘high’ HA groups. Median survival in the ‘high’ Col I group was 6.4 months, as opposed to 14.6 months for the ‘low’ Col I group. The median difference was 8.2 months.

Figure 2

Histochemical staining for stromal content of adjacent normal, primary tumor, and metastatic lesions. Representative images are shown of patient tissue sections stained by both standard H&E and Movat’s pentachrome staining techniques. Representative images of cytokeratin and α-smooth muscle actin staining are also shown. Significant desmoplasia is seen in both tumor and liver metastases, but not in adjacent normal tissues. (Scale bar=100μm)

Figure 3

Immunohistochemical assessment of collagen and HA expression in PDAC tissues. Patient tissues sections were stained with antibodies for Collagens I, III, IV, and HA. Representative images are shown of adjacent normal, primary tumor, and metastatic lesions. (Scale bar=100μm)

Figure 4

Representative images of patient matched pancreatic primary and metastatic lesions stained for Collagen I, and quantitative assessment of stromal content of all primary tumors and metastatic lesions. Patient tissue sections (left panel) from confirmed cases of ductal adenocarcinoma were stained for Collagen I. Tumors and their matched metastatic lesions from three patients are displayed. Primary tumors and metastatic lesions show similar levels of Collagen I staining. Metastatic lesions shown were excised from the lymph node (sample 1), liver (sample 2), and mesentery (sample 3). (Scale bar=100μm) For comparison, sample scoring is shown in Table 2 (corresponding to samples 2, 3, and 4). In our quantitative assessment (right panel), the percent area of positive Collagen I staining was plotted for each case and grouped into primary tumor and metastases for comparison.