Growth Patterns and Angiogenesis in Primary Breast Cancer

It has become evident that tumor growth cannot be understood without considering the interactions between the tumor cells and the components of the stromal microenvironment, such as the vasculature. Much research has been devoted to determining the impact of neovascularization— that is, angiogenesis—on tumor progression. Many authors have investigated the prognostic value of quantifying tumor vascularity. Although some contradictory results have been published, mainly due to differences in methodology, almost all studies with multivariate analysis that used either CD31 or CD34 for immunostaining the vessels showed a significant association between high tumor vascularity and unfavorable clinical outcome.

The recommended methodology of angiogenesis quantification has been described in an international consensus report [1]. It is unlikely, however, that this methodology will ever be applied to every breast carcinoma in routine pathology practice if more practical surrogate markers can be used to estimate tumor vascularity. Histological surrogate markers should give a reliable, fast, and easy estimate of the amount of angiogenesis in a tumor. Ideally, a standard his-tochemical technique, such as a hematoxylin-eosin stain, should suffice. Interpretation of the slides should not rely on extensive training and should not be time-consuming. Yet, a clear pathophysiological mechanism should corroborate the association of these markers with parameters directly reflecting angiogenesis, such as microvessel density and the fraction of proliferating endothelial cells.

Two candidate surrogate markers of angiogenesis are the fibrotic focus and the growth pattern.

A fibrotic focus (Figure 1) was proposed in 1996 [2] as an indicator of tumor aggressiveness in invasive ductal carcinoma of the breast. It appears as a central, radially expanding fibrosclerotic core and consists of loose, dense, or hyalinized collagen bundles, a variable number of fibrob-lasts, blood vessels, and inflammatory cells. It shows many similarities with granulation tissue and subsequent scar formation in wound repair and can be regarded as a focus of exaggerated reactive tumor stroma formation.

Different growth patterns have been shown to reflect differences in angiogenesis, both in lung tumors and in liver metastases [3, 4]. In invasive breast carcinoma, we defined two different growth patterns: An expansive carcinoma is a

Figure 1 Expansively growing carcinoma of the breast containing a large fibrotic focus. The tumor shows a pushing margin (right) and a central area of fibrous scar-like tissue, the fibrotic focus (left).

well-circumscribed tumor consisting of carcinoma cells and reactive tumor stroma without intervening preexisting structures, whereas an infiltrative carcinoma consists of carcinoma cells infiltrating between preserved normal structures. Tumors consisting of a central expansive nodule with infil-trative tumor at the periphery are included in the expansive category. The association of these growth patterns with other prognostic features was studied in 104 T1-2N0M0 breast carcinoma patients (Table I). An expansive growth pattern was most often observed in ductal carcinomas with poor histological differentiation and brisk mitotic activity. Necrosis was rarely present in carcinomas with an infiltra-tive growth pattern, and the presence of a fibrotic focus was also significantly less frequent in these tumors than in the expansive ones. Necrosis and fibrotic foci are routine histological markers of intratumoral hypoxia. This has been confirmed by studying the expression of the endogenous hypoxia marker carbonic anhydrase IX (CA IX) in a group of 184 breast cancer patients [5]. CA IX expression in carcinoma cells and in intratumoral fibroblasts was significantly associated with the presence of a fibrotic focus. Intratumoral hypoxia is assuming growing importance in the pathogene-sis of neoplastic progression. In addition to being a driver of angiogenesis, some genes controlling this process being

Table I Correlation of Growth Pattern with Other Variables in 104 T1-2N0M0 Breast Cancer Patients.

Variable

Expansive growth

Infiltrative growth p-value

Histological type

Histological grade

Well differentiated (n = 31) Moderately differentiated (n = 33) Poorly differentiated (n = 28)

Mitotic activity index (MAI)

Necrosis

Fibrotic focus

Present (n = 55) Absent (n = 49) CA IX score in carcinoma cells CA IX score in intratumoral fibroblasts Tumor vascularity Chalkley max Chalkley mean

2 62

18 19 25

19 45

45 19

10 30

14 3

10 30

0.004

Adapted from Colpaert, C. G., et al. (2001). J. Pathol. 193, 442-449.

For continuous variables, figures are mean ± standard deviation (median).

MAI: mitotic activity index; the number of mitotic figures per 10 high-power fields of the microscope (magnification 400x).

CAIX: Carbonic anhydrase IX; an endogenous marker of hypoxia. Its expression is semiquantitatively scored as the product of the percentage of immunostained cells with an immunostaining intensity score ranging from 0 (no staining) to 3 (strong staining).

Chalkley count: Point overlap morphometric technique to quantify the relative area occupied by vessels in a vascular "hot spot," that is, an area of high vascular density. Chalkley max is the count obtained in the most vascular hot spot; Chalkley mean is the mean of the three highest counts.

oxygen regulated, hypoxia induces proteomic and genetic changes that promote an aggressive tumor phenotype.

Expression of the hypoxia marker CA IX was significantly more pronounced in expansively growing tumors than in infiltrative ones (Table I). The assumption is that the latter are less hypoxic because the tumor cells grow along preexisting well-formed blood vessels that are probably more efficient in providing oxygen and nutrients to the tumor than newly formed vessels. Therefore, the necessity to initiate angiogenesis is less pronounced in infiltrative tumors than in expansive ones, which is reflected by the significantly lower vascular density (estimated by Chalkley counting; see Table I) in the infiltrative tumors. The presence of a fibrotic focus is also significantly associated with vascular density estimated by Chalkley counting [6] and with high endothelial cell proliferation fractions [5]. Both growth pattern and fibrotic focus can therefore be used as routine histopathological surrogate markers of hypoxia-driven angiogenesis.

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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