No common denominator for breast cancer lymph node metastasis

Abstract

The axillary lymph node status is the most powerful prognostic factor for breast cancer patients to date. The molecular mechanisms that control lymph node metastasis, however, remain poorly understood. To define patterns of genes or gene regulatory pathways that drive breast cancer lymph node metastasis, we compared the gene expression profiles of 15 primary breast carcinomas and their matching lymph node metastases using microarrays. In general, primary breast carcinomas and lymph node metastases do not differ at the transcriptional level by a common subset of genes. No classifier or single gene discriminating the group of primary tumours from those of the lymph node metastases could be identified. Also, in a series of 295 breast tumours, no classifier predicting lymph node metastasis could be developed. However, subtle differences in the expression of genes involved in extracellular-matrix organisation and growth factor signalling are detected in individual pairs of matching primary and metastatic tumours. Surprisingly, however, different sets of these genes are either up- or downregulated in lymph node metastases. Our data suggest that breast carcinomas do not use a shared gene set to accomplish lymph node metastasis.

Figure 1

(A) Unsupervised hierarchical clustering of 30 primary breast carcinomas and lymph node metastases from 15 patients, measured over 18 336 genes. The dendrogram has two large branches; the orange bar represents ER-α-negative and the green bar ER-α-positive tumours. Alignment of all matching pairs was established. (B) Permutation test of the WPBPSR. Blue: null hypothesis distribution. Distribution after randomisation of the labels of the primary and metastatic tumours, repeated 20 000 times (WPBPSR=1±0.05). The red line represents the WPBPSR of the 15 matching pairs (WPBPSR=0.45; P<0.0001). Prim=primary tumour; LNmeta=lymph node metastasis; Prim n, LNmeta n (n=1–17)=patient number primary tumour, patient number lymph node metastasis, respectively.

Figure 2

Haematoxylin and eosin staining of two paraffin-embedded primary infiltrative ductal breast carcinomas and their matching lymph node metastases (× 5). (A, C) Normal mammary gland tissue next to tumour cells. (B, D) The lymph node capsule adjacent to tumour cells. S=stromal cells; T=tumour cells.

Figure 3

Unsupervised hierarchical clustering of eight primary breast carcinomas, obtained from four patients with two primary tumours, and matching metastases, measured over 18 336 genes. Alignment of primary tumours with their metastases, not with the second primary tumour, is shown. Prim=primary tumour; LNmeta=lymph node metastasis; Meta=distant metastasis; Prim n, LNmeta/Meta n (n=18, 21, 23, 24)=patient number primary tumour, patient number metastasis, respectively; Prim nA, Prim nB=two primary tumours; LNnA/B=lymph node metastasis developed from primary tumour A or B.

Figure 4

Relative quantity of expression of (A) CXCR4, (B) CXCL12 and (C) VEGF-C and VEGF-D in primary breast carcinomas, lymph node metastases and various normal tissues. LN=lymph node. Primary tumours LN metastases=primary breast carcinomas that developed lymph node metastases only; primary tumours distant metastases=primary breast carcinomas that developed distant metastases only; primary tumours distant and LN metastases=primary breast carcinomas that developed distant and lymph node metastases; primary tumours no metastases=primary breast carcinomas that developed no metastases. The median expression level for each marker gene within a group is indicated by a horizontal line.