Circulating tumour cells: the evolving concept and the inadequacy of their enrichment by EpCAM-based methodology for basic and clinical cancer research

Increasing evidence suggests that circulating tumour cells (CTCs) are responsible for metastatic relapse and this has fuelled interest in their detection and quantification. Although numerous methods have been developed for the enrichment and detection of CTCs, none has yet reached the 'gold' standard. Since epithelial cell adhesion molecule (EpCAM)-based enrichment of CTCs offers several advantages, it is one of the most commonly used and has been adapted for high-throughput technology. However, emerging evidence suggests that CTCs are highly heterogeneous: they consist of epithelial tumour cells, epithelial-to-mesenchymal transition (EMT) cells, hybrid (epithelial/EMT(+)) tumour cells, irreversible EMT(+) tumour cells, and circulating tumour stem cells (CTSCs). The EpCAM-based approach does not detect CTCs expressing low levels of EpCAM and non-epithelial phenotypes such as CTSCs and those that have undergone EMT and no longer express EpCAM. Thus, the approach may lead to underestimation of the significance of CTCs, in general, and CTSCs and EMT(+) tumour cells, in particular, in cancer dissemination. Here, we provide a critical review of research literature on the evolving concept of CTCs and the inadequacy of their enrichment by EpCAM-based technology for basic and clinical cancer research. The review also outlines future perspectives in the field.

Dipeptidase 1: a candidate tumor-specific molecular marker in colorectal carcinoma

The aim of this study was to identify tumor-specific markers for the detection of rare disseminated colorectal tumor cells in peripheral venous blood and in intra-peritoneal saline lavage samples collected before and after resection of colorectal tumors. Using cDNA micro-array screening, we found dipeptidase 1 (DPEP1) to be highly expressed in colon tumors compared to matched normal mucosa. Relative reverse transcriptase (RT)-PCR showed that DPEP1 was over-expressed by >/=2 fold in colon tumor compared to normal colonic mucosal tissue in 56/68 (82%) patients. Using immunobead RT-PCR, a technique that first enriches for epithelial cells, we found DPEP1 positive cells in intra-peritoneal lavage and venous blood samples from 15/38 (39%) colorectal cancer cases. This is the first report of DPEP1 as a marker for disseminated colon tumor cells.

Molecular detection of blood-borne epithelial cells in colorectal cancer patients and in patients with benign bowel disease

In colorectal cancer (CRC), a proportion of patients with early stage disease still die of metastatic or recurrent disease within 5 years of "curative" resection. Detection of carcinoma cells in the peripheral circulation at presentation may identify a subgroup of patients with micro-metastatic disease who may benefit from adjuvant chemotherapy or radiotherapy. Our aim was to determine the presence and clinical significance of colon carcinoma cells in peripheral blood at the time of surgery. Preoperative peripheral blood samples were collected from 94 patients with CRC and 64 patients undergoing bowel resection for benign conditions (adenoma, diverticular disease or Crohn's colitis). Blood was also obtained from 20 normal donors not undergoing bowel surgery. Immunomagnetic beads were used to isolate epithelial cells followed by reverse transcription-polymerase chain reaction (RT-PCR) analysis of expression of cytokeratin (CK) 19, CK 20, mucin (MUC) 1 and MUC 2. Nineteen of 94 (20%) CRC patients were positive for epithelial cells in preoperative blood, including 6 with early stage disease. Kaplan-Meier survival analysis showed that detection of epithelial cells in preoperative blood was associated with reduced disease-free and overall survival (log-rank test, p = 0.0001). Surprisingly, circulating epithelial cells were detected in 3/30 (10%) patients resected for adenoma, and in 4/34 (12%) patients resected for benign inflammatory conditions, suggesting that cells from nonmalignant colonic epithelium may also gain entry into the bloodstream in the presence of bowel pathology. All 20 normal control bloods were negative for epithelial cells.

Somatic mutations, acetylator status, and prognosis in colorectal cancer

BACKGROUND

Somatic mutations in K-ras and TP53 may be associated with both acetylator status and prognosis in colorectal cancer.

AIMS

To determine whether cancers with somatic mutations are more frequent in fast acetylators and whether mutations or acetylator status influence prognosis after colorectal surgery.

PATIENTS

One hundred consecutive subjects undergoing elective surgery for colorectal cancer.

METHODS

Acetylator status was determined by polymerase chain reaction (PCR) genotyping for polymorphism in the N-acetyltransferase 2 (NAT2) gene. Mutations in K-ras (codon 12) and TP53 were determined by PCR analysis using restriction enzyme digestion and single strand conformation polymorphism respectively. Survival from colorectal cancer for up to five years after diagnosis was analysed using the Kaplan-Meier product limit estimator. Cox proportional hazards regression was used to compare survival rates after adjusting for tumour stage.

RESULTS

Mutations in K-ras and TP53 were independent of acetylator status. By log rank test, survival was significantly reduced in subjects with TP53 mutations (p = 0.003) but was not significantly related to acetylator status or the presence of K-ras mutations. After adjustment for tumour stage, subjects with both TP53 and K-ras mutations had a 4.2-fold case fatality (95% confidence interval 1.5 to 11.6) when compared with that of a TP53 negative reference group.

CONCLUSION

The presence of both TP53 and K-ras mutations in colorectal tumours is an adverse prognostic marker which is independent of tumour stage.

Detection of Circulating Tumor Cells Using lmmunobead-PCR

Many studies have shown that survival following surgery for solid tumors, such as colorectal and breast, is influenced by the extent of local invasion and the presence of distant metastases, and staging systems based on that are still the main prognostic indicator of survival. However, 20-30% of patients with early stage disease, without evidence of lymph node or distant dissemination, relapse and die within 5 yr of "curative" resection. The inference is that occult or micrometastatic disease was already present at the time of resection, or that tumor cells with metastatic potential were released into the blood stream as a result of surgery. Detection of circulating tumor cells at diagnosis in early stage patients would imply that the disease is more advanced than indicated by conventional staging. These patients might then be offered adjuvant chemotherapy or radiotherapy post surgery.

Immunobead RT-PCR: a sensitive method for detection of circulating tumor cells

Detection of circulating tumor cells and micrometastases in patients with cancer should prove useful in determining prognosis and in planning and monitoring systemic therapies. We have developed immunomagnetic isolation of carcinoma cells followed by reverse transcription polymerase chain reaction (immunobead RT-PCR) as a method for identifying very small numbers of breast cancer cells in blood. The expression of cytokeratin 19 (K19) was used as the marker by which the isolated tumor cells were identified. The immunobead RT-PCR technique allowed detection of one tumor cell per 10(6) leukocytes in whole blood. Immunobead RT-PCR is a highly sensitive method of detecting cancer cells in a hematopoietic environment.

Detection of circulating tumor cells in colorectal cancer by immunobead-PCR is a sensitive prognostic marker for relapse of disease

BACKGROUND

Recurrent and metastatic carcinoma of the colorectum remains a major problem, with survival at 5 years post curative resection still only about 50%. Moreover, up to 30% of patients who present with early stage disease also relapse and die within 5 years, suggesting the presence of micrometastatic disease at diagnosis. One route of metastatic spread is via the blood stream, hence the detection of tumor cells in blood is likely to provide an important predictive tool with respect to relapse of disease. We have developed a sensitive molecular technique to identify tumor cells in blood using mutations in codon 12 of the K-ras gene as a marker.

MATERIALS AND METHODS

Twenty-seven patients whose tumor carried a mutation in codon 12 of K-ras were studied for the presence of tumor cells in perioperative peripheral blood samples. Immunomagnetic beads, labeled with an epithelial-specific antibody, were used to harvest epithelial cells from blood. K-ras mutations were identified in this selected population using a polymerase chain reaction (PCR)-based analysis (immunobead-PCR).

RESULTS

Circulating K-ras mutant cells were detected in 9 or 27 patients; seven of these nine patients have since died due to recurrent or metastatic disease. Mutant cells were not detected in 18 patients, and 16 or 18 have remained disease free (median follow-up: 16 months; range: 7-42 months). Kaplan-Meier analysis showed that detection of K-ras mutant cells in bloods was associated with significantly reduced disease-free survival (p = 0.0001).

CONCLUSION

This study indicates that detection of circulating tumor cells perioperatively by immunobead-PCR provides a sensitive prognostic marker for recurrent and metastatic colorectal cancer.

Significance of molecular marker-positive cells after autologous peripheral-blood stem-cell transplantation for non-Hodgkin's lymphoma

PURPOSE

To evaluate the significance of molecular marker-positive cells in a cohort of non-Hodgkin's lymphoma (NHL) patients undergoing high-dose chemotherapy and autologous peripheral-blood stem-cell transplantation (PBSCT).

PATIENTS AND METHODS

Twenty-eight PBSC transplants have been performed in 24 patients with poor-prognosis NHL. Molecular analysis of the t(14;18) (q32;q21) translocation (bcl-2/immunoglobulin [Ig] heavy-chain joining locus [JH] fusion) or antigen receptor gene rearrangements was performed to determine the presence of lymphoma cells at presentation, in PBSC harvests, and before and after autologous PBSCT. Kaplan-Meier estimates of survival and Cox regression analyses were used to test the effect of bone marrow involvement, tumor-cell contamination of PBSCs, disease stage, and chemotherapy sensitivity at transplantation, and presence of marker-positive cells post-PBSCT on disease-free and overall survival.

RESULTS

Thirteen of 24 patients (54%) are alive following PBSCT at a median follow-up time of 654 days (range, 193 to 1,908). Nine patients are in complete remission (CR) at day 216 to 1,799 (median, 805) and four are alive following relapse (day 440, 573, 1,188, and 1,908). Eleven patients (46%) have died: three of transplant-related complications at day 0, 1, and 13, and eight of recurrent disease (day 132 to 1,330; median, 451). Longitudinal marker studies post-PBSCT showed that of 16 relapse events, 13 (81%) were positive for the lymphoma marker at or before clinically documented relapse. Marker studies became negative post-PBSCT in nine of nine patients who entered and remained in CR. Disease-free survival (DFS) was significantly shortened in patients in whom marker-positive cells were detected in serial samples posttransplantation (P = .006). Cox regression analysis showed that patients in this group had a 24 times higher risk of relapse (P = .03).

CONCLUSION

The results show that the reappearance or persistence of marker-positive cells after autologous PBSCT is strongly associated with relapse.

Immunobead-PCR: a technique for the detection of circulating tumor cells using immunomagnetic beads and the polymerase chain reaction

The presence of tumor cells in the circulation may predict disease recurrence and metastases. We have developed a sensitive technique for the detection of carcinoma cells in blood, using immunomagnetic beads to enrich for epithelial cells and the polymerase chain reaction to identify a tumor marker. The colon carcinoma cell line SW480, homozygous for a K-ras codon 12 mutation, was used to establish optimal conditions. The SW480 cells were serially diluted in normal blood and incubated with immunomagnetic beads labeled with a monoclonal antibody specific for epithelial cells. Cells bound to the beads were retrieved using a magnetic field and the presence of K-ras codon 12 mutations determined by a polymerase chain reaction based analysis. SW480 cells could be detected in dilutions up to 1 SW480 cell/10(5) leukocytes in whole blood.

Molecular detection of residual lymphoma cells in peripheral blood stem cell harvests and following autologous transplantation

Twenty-seven patients with non-Hodgkin's lymphoma (NHL) have undergone peripheral blood stem cell (PBSC) harvesting for autologous transplantation (Tx). A molecular marker was found at presentation in 23/27 patients. Immunoglobulin heavy chain (IgH) or T cell receptor beta (TCR beta) rearrangements were detected by Southern blotting or the polymerase chain reaction (PCR) in 13 patients; PCR detected the bcl-2/JH fusion in 10 patients. Fifteen autologous PBSC transplants have been performed in 11 patients. In 5/11 patients, the marker was present in at least one PBSC collection (in four patients, every PBSC collection was positive). Survival data are available for nine patients (two early deaths); three patients relapsed and died (221 - 930 d), one is alive and in relapse (354 + d) and five are alive and in complete remission (330 - 1290 + d). These findings suggest that tumour cell contamination of PBSC harvests is not uncommon. Whether these cells are clonogenic and contribute to disease relapse remains to be elucidated. The presence of residual disease at the time of transplantation and the reappearance (or persistence) of marker positive cells post-transplantation both appear to be poor prognostic factors for disease-free survival.

A rare translocation (4;11)(q21;p14-15) in an acute lymphoblastic leukemia expressing T-cell and myeloid markers

A 21-year-old male presented with a large mediastinal mass and a white cell count of 420 x 10(9)/L. A diagnosis of acute lymphoblastic leukemia (ALL) was made, with 90% of cells in the bone marrow (BM) and 99% in the peripheral blood (PB) being lymphoblasts (FAB L1). Cytogenetic analysis of these cells revealed a rare variant of the t(4;11) translocation involving chromosome arm 11p rather than 11q, namely t(4;11)(q21;p14-15). The standard form of the (4;11) translocation has been associated with leukemias with mixed-lineage phenotypes. Three cases of ALL with t(4q;11p) have previously been reported. One of these cases showed phenotypic heterogeneity involving myeloid and lymphoid lineages. The leukemia reported here also exhibits lymphoid/myeloid features. Immunophenotyping of the blasts showed that most of the cells were positive for CD2, CD5, CD7, CD10 (CALLA), CD34, and HLA-DR. A significant proportion of the cells expressed CD33. These results suggest a biphenotypic rather than a biclonal disease. Molecular analysis showed rearrangement of both immunoglobulin heavy-chain genes (JH) and of a single allele of the T-cell receptor (TCR) gamma 1 gene, while retaining germline TCR beta genes.