From latent disseminated cells to overt metastasis: Genetic analysis of systemic breast cancer progression

Abstract

According to the present view, metastasis marks the end in a sequence of genomic changes underlying the progression of an epithelial cell to a lethal cancer. Here, we aimed to find out at what stage of tumor development transformed cells leave the primary tumor and whether a defined genotype corresponds to metastatic disease. To this end, we isolated single disseminated cancer cells from bone marrow of breast cancer patients and performed singlecell comparative genomic hybridization. We analyzed disseminated tumor cells from patients after curative resection of the primary tumor (stage M0), as presumptive progenitors of manifest metastasis, and from patients with manifest metastasis (stage M1). Their genomic data were compared with those from microdissected areas of matched primary tumors. Disseminated cells from M0-stage patients displayed significantly fewer chromosomal aberrations than primary tumors or cells from M1-stage patients (P < 0.008 and P < 0.0001, respectively), and their aberrations appeared to be randomly generated. In contrast, primary tumors and M1 cells harbored different and characteristic chromosomal imbalances. Moreover, applying machine-learning methods for the classification of the genotypes, we could correctly identify the presence or absence of metastatic disease in a patient on the basis of a single-cell genome. We suggest that in breast cancer, tumor cells may disseminate in a far less progressed genomic state than previously thought, and that they acquire genomic aberrations typical of metastatic cells thereafter. Thus, our data challenge the widely held view that the precursors of metastasis are derived from the most advanced clone within the primary tumor.T he prevailing paradigm of carcinogenesis suggests that epithelial cells sequentially accumulate multiple genetic and epigenetic changes underlying the disorganization of tissue morphology and uncontrolled growth (1). The model predicts that certain additional genomic events initiate invasiveness of the tumor and subsequently progression to metastasis. However, this hypothesis of an ''additional event'' initiating metastasis relatively late in tumorigenesis was recently challenged by another model based on global gene expression analysis of primary breast cancers in which groups of genes were identified that predicted the development of distant metastasis (2). Thus it was concluded that the proclivity to metastasize is acquired early during multistep tumorigenesis, although it manifests only much later after mutation of other genes (3).A closer analysis of the natural course of breast cancer reveals several inconsistencies with both models. Why, after curative resection of a primary tumor and its regional lymph nodes, does it often take years or decades until clinical metastases appear? It is difficult to understand how a cell that has been selected at the primary site for acquisition of self-sufficiency in growth signals, unlimited proliferative potential, sustained angiogenesis, and unresponsiveness to growth inhibitory signals...

HER2 status of bone marrow micrometastasis and their corresponding primary tumours in a pilot study of 27 cases: a possible tool for anti-HER2 therapy management?

“…Our results and these published data on the stability of HER2 status between primary and metastatic tumours are in contrast with the recently published studies by Schmidt-Kittler et al (2003) and by Klein et al (Mercapide et al 2002) showing that micrometastatic cells demonstrated fewer chromosomal alterations, such as losses and gains detected by single-cell CHG analysis, than primary tumour cells (Mercapide et al 2002;Schmidt-Kittler et al, 2003). Another recently published study also showed that HER2 amplification was more frequently observed in circulating cells than in primary tumours and therefore concluded that HER2 amplification could be acquired during the metastatic process (Meng et al, 2004).…”

Dynamics of chemosensitivity and chromosomal instability in recurrent glioblastoma

“…Correspondingly, Schmidt-Kittler et al (2003) have reported an early dissemination of single breast cancer cells with different chromosomal aberrations from the primary tumour to the surrounding healthy tissue. Absence of several alterations detected in the primary tumour suggested dissemination not only from the most advanced clone but also from pre-stages before immortalisation (Schmidt-Kittler et al, 2003). Alternatively, one might hypothesise that BTL3 is not derived from BTL1 but represents a second unrelated metachronous glioblastoma as has been reported before (Inda et al, 2003).…”

FIP200, a key signaling node to coordinately regulate various cellular processes

“…In all seven cases, both FIP200 alleles were inactivated with two primary breast cancers containing compound heterozygous deletions in both alleles and the other five showing loss of heterozygosity (LOH) of FIP200 [31]. Furthermore, LOH of FIP200 was also observed in several primary breast cancer samples in another study [50]. These genetic data thus provide evidence that FIP200 might function as a tumor suppressor gene.…”