Immunocytologic detection of isolated tumor cells in bone marrow of patients with squamous cell carcinomas of the head and neck region

Clinical applications of liquid biopsy in HPV‐negative and HPV‐positive head and neck squamous cell carcinoma: advances and challenges

Head and neck squamous cell carcinomas (HNSCCs) represent the most common epithelial tumors that arise from mucosa of the oral cavity, pharynx, and larynx. The development of HNSCCs is usually associated with tobacco use, alcohol consumption, and human papillomavirus (HPV) infection. Most HNSCCs are diagnosed in advanced states, leading to a worse clinical outcome. Screening tests based on potential biomarkers associated with HNSCCs could improve this scenario. Liquid biopsy has emerged as a promising area of cancer investigation, offering a minimally invasive approach to track circulating biomarkers in body fluids that could potentially contribute to the diagnosis, predict prognosis, and monitor response to treatment. This review will discuss translational studies describing the clinical applications of liquid biopsy in HPV-negative and HPV-positive HNSCCs focused on circulating nucleic acids [cell-free DNA (cfDNA) and cell-free RNA (cfRNA)], circulating tumor cells (CTCs), and extracellular vesicles (EVs), which can be found in plasma, serum, and saliva.

Cytokeratin 17 mRNA as a prognostic marker of oral squamous cell carcinoma

Despite diagnostic and therapeutic advances, the 5-year survival rate of oral squamous cell carcinoma (OSCC) remains between 70–80% due to recurrences and secondary metastases to cervical lymph nodes. It is difficult to find these recurrences and metastases postoperatively, thus, careful follow-up is recommended. Cytokeratins (CKs) are intermediate filaments of the cytoskeleton and candidate prognostic biomarkers for OSCC, as they are overexpressed in OSCC compared with normal mucosa. The aim of the present study was to determine the relative levels of occurrence of 3 CK mRNA (CK17, CK19, CK20) transcripts in peripheral blood mononuclear cells (PBMC) using reverse transcription-quantitative polymerase chain reaction. The study comprised pre- and post-operative PBMC samples from 19 OSCC patients. In the good-prognosis group, 10 of 13 patients demonstrated reduced CK17 mRNA expression post-operatively, compared with pre-operative samples, conversely, only 3 of 6 patients in the poor-prognosis group had reduced post-operative CK17 mRNA expression. This difference was statistically significant (P<0.01). The disease-free survival rate of the group with reduced post-operative CK17 mRNA expression was significantly increased compared with the elevated CK17 mRNA group (P<0.01); however, the overall survival rates of the two groups were not significantly different. Neither CK19 mRNA nor CK20 mRNA were significantly expressed in the PBMC of OSCC patients. Overall, CK17 mRNA expression may be a useful prognostic biomarker for OSCC.

VEGFR-1 expression levels predict occurrence of disseminated tumor cells in the bone marrow of patients with esophageal carcinoma

Blocking angiogenesis by inhibiting VEGF represents an established therapeutic strategy in many cancers. The role of placental growth factor (PlGF) and of its receptor VEGFR-1 in tumor biology remain more elusive. Currently, humanized monoclonal antibodies against PlGF are studied in early phase clinical trials because PlGF inhibition blocked murine tumor growth and angiogenesis. In contrast to mice exclusively expressing one PlGF isoform (PlGF-2), humans can produce four PlGF isoforms (PlGF1-4). Surprisingly nothing is yet known about expression of all four PlGF isoforms in human cancer, because until now mostly total PlGF levels or PlGF-1/2 were analyzed without discriminating further. In this study we determined mRNA expression levels of PlGF1-4 and of VEGFR-1 by QRT-PCR in human esophageal tumor tissue and investigated whether gene expression levels correlate with clinical data. PlGF-1 and -2 were expressed in virtually all analyzable tumors, whereas PlGF-3 and -4 were present in tumors of 59 and 74 % of patients, respectively. MRNA Expression levels of all four splice variants correlated with each other. In contrast, PlGF-1 and -2 mRNA expression was lower in esophageal control tissue and PlGF-3 and -4 mRNA were undetectable. VEGFR-1 was expressed by more than 80 % of patients. Interestingly, VEGFR-1 expression levels significantly correlate with presence of disseminated tumor cells (DTCs) in bone marrow. Patients with DTCs exhibit lower VEGFR-1 mRNA expression than patients without DTCs. Pending validation in other types of cancer, expression levels of VEGFR-1 might be useful as surrogate marker for DTCs.

Review: Biological relevance of disseminated tumor cells in cancer patients

The prognosis of cancer patients is largely determined by the occurrence of distant metastases. In patients with primary tumors, this relapse is mainly due to clinically occult micrometastasis present in secondary organs at primary diagnosis but not detectable even with high resolution imaging procedures. Sensitive and specific immunocytochemical and molecular assays enable the detection and characterization of disseminated tumor cells (DTC) at the single cell level in bone marrow (BM) as the common homing site of DTC and circulating tumor cells (CTC) in peripheral blood. Because of the high variability of results in DTC and CTC detection, there is an urgent need for standardized methods. In this review, we will focus on BM and present currently available methods for the detection and characterization of DTC. Furthermore, we will discuss data on the biology of DTC and the clinical relevance of DTC detection. While the prognostic impact of DTC in BM has clearly been shown for primary breast cancer patients, less is known about the clinical relevance of DTC in patients with other carcinomas. Current findings suggest that DTC are capable to survive chemotherapy and persist in a dormant nonproliferating state over years. To what extent these DTC have stem cell properties is subject of ongoing investigations. Further characterization is required to understand the biology of DTC and to identify new targets for improved risk prevention and tailoring of therapy. Our review will focus on breast, colon, lung, and prostate cancer as the main tumor entities in Europe and the United States.

Detection of Micrometastatic Disease in Bone Marrow: Is It Ready for Prime Time?

Minimal residual disease (MRD), or isolated tumor cells (ITCs) in bone marrow, may be the source of potentially fatal overt distant metastases in solid tumors even years after primary treatment. MRD can be detected by immunohistochemical methods using antibodies directed against cytokeratins or cell-surface markers or molecular, polymerase chain reaction-based techniques. Among solid tumors, the clinical relevance of MRD has been most extensively studied in breast cancer patients. Recently, the highest level of evidence for the prognostic impact of MRD in primary breast cancer was reached by a pooled analysis comprising more than 4,000 patients, showing poor outcome in patients with MRD at primary therapy. Yet the clinical application of MRD detection is hampered by the lack of a standardized detection assay. Moreover, clinical trial results demonstrating the benefit of a therapeutic intervention determined by bone marrow status are still absent. Recent results suggest that, in addition to its prognostic impact, MRD can be used for therapy monitoring or as a potential therapeutic target after phenotyping of the tumor cells. Persistent MRD after primary treatment may lead to an indication for extended adjuvant therapy. However, until clinically relevant data regarding successful therapy of MRD are available, treatment interventions on the basis of MRD should only be performed within clinical trials.

Molecular markers for diagnosis and prognosis

A plethora of aberrations are associated with progress and outcome for head and neck cancer patients and some have been shown to provide prognostic information independent of the TNM staging system. These findings justify future studies that will harness recent advances in technologies to refine the range of molecular markers available. Important lessons have been learnt during the last two decades, particularly the need to perform multivariate analysis and to combine information derived from several molecular markers. At present the overall evidence is insufficient to alter clinical practice or to consider restricting clinical trials of new adjuvant to subsets of patients, identified on the basis of the use of molecular markers. However, a number of key prospective clinical studies are in progress and we can be optimistic that in the near future clinical research incorporating specific markers may provide new criteria for defining risk of relapse or of developing a new primary tumour, and guide the choice of optimal adjuvant treatment after surgery. The only way to truly validate a marker is to incorporate it into large clinical trials, and it is anticipated that the new treatment options that are on the horizon, that are likely to be an improvement on radiotherapy alone, will provide opportunities to help translate this laboratory research into clinical practice.

Clinical Significance of Micrometastatic Cells Detected by E48 (Ly-6D) Reverse Transcription-Polymerase Chain Reaction in Bone Marrow of Head and Neck Cancer Patients

PURPOSE

Despite improvements in locoregional treatment of head and neck squamous cell carcinoma (HNSCC), local and distant failure rates remain high. The strongest prognostic indicator of HNSCC is the presence of lymph node metastases in the neck, but the value of this indicator has limitations when using for the individual patient. The presence of micrometastatic cells in bone marrow has been shown to be a putative prognostic indicator in HNSCC and other epithelial malignancies, which might allow more accurate staging and selection of patients for whom adjuvant or experimental therapy is recommended. The gene encoding the E48 antigen is selectively expressed by HNSCC, and the detection of E48 transcripts in bone marrow by reverse transcription-polymerase chain reaction (RT-PCR) presumably represents the presence of micrometastatic cells. The purpose of this study was to determine the association between the presence of micrometastatic cells in bone marrow of HNSCC patients and clinical outcome.

EXPERIMENTAL DESIGN

A total of 162 patients treated surgically for primary HNSCC underwent a single bone marrow aspiration from the upper iliac crest for detection of micrometastatic cells using E48 RT-PCR. In total, 139 patients were evaluable. The primary statistical endpoints were disease-free survival and distant metastasis-free survival. In addition, bone marrow samples of 30 noncancer controls were evaluated.

RESULTS

E48 RT-PCR indicated the presence of micrometastatic cells in the bone marrow in 56 of 139 (40%) of the HNSCC patients and 0 of 30 of the noncancer controls (P < 0.0001). The presence of micrometastatic cells had no significant influence on disease-free survival or distant metastasis-free survival for the whole group of HNSCC patients (P = 0.1460 and P = 0.2912, respectively). For patients with >or=2 lymph node metastases, however, the presence of micrometastatic cells was associated with a poor distant metastasis-free survival (P = 0.0210).

CONCLUSIONS

The presence of micrometastatic cells in bone marrow of HNSCC patients with >or=2 lymph node metastases is correlated with a poor distant metastasis-free survival. In this subgroup of HNSCC patients, E48 RT-PCR seems to be a valuable tool to identify patients who are at increased risk for development of distant metastases and therefore might benefit from experimental adjuvant systemic therapy.

Detection of bone marrow micrometastases in the rib marrow of head and neck cancer patients: a prospective pilot study

Flow cytometry has been validated as an objective method of demonstrating and quantifying micrometastases. Micrometastases within bone marrow indicate a poor prognosis in patients with upper gastrointestinal, colorectal and breast epithelial tumours. We prospectively sought to assess the feasibility of testing rib marrow for bone marrow micrometastases in head and neck cancer and to report their frequency in a cohort of patients. Nine patients were enrolled in the study. Bone marrow was obtained before manipulation of the primary tumour. Micrometastatic cells were detected by staining contaminant cytokeratin-18 positive cells and using the twin techniques of immuncytochemistry and flow cytometry. Cellular marrow was retrieved in 100% of cases. Micrometastases were detected in one out of nine epithelial tumours on both flow cytometry and immunocytochemistry. The detection rate appeared to be independent of TN staging. We were unable to culture the cells. Preoperative detection of bone marrow micrometastases may reflect transient shedding of cells, metastatic potential or residual disease. This prospective study confirms the feasibility of using rib marrow in future studies investigating micrometastases in head and neck cancer.

Molecular diagnosis of head and neck cancer

Patients with advanced stages of head and neck cancer frequently develop locoregional recurrence as well as distant metastases. These data indicate that traditional diagnostic methods such as histopathology and radiology are not sensitive enough to detect the small numbers of tumor cells which are left behind, defined as minimal residual disease (MRD). Sensitive diagnostic assays based on molecular markers appear to be powerful tools to improve the staging of these patients. At the DNA level, tumor-specific p53 mutations seem to have great potential for the detection of "occult" tumor cells at surgical margins and lymph nodes. At the RNA level HNSCC associated antigens like the E48 antigen, allow the detection of rare HNSCC cells in blood and bone marrow and, it is hoped, also in lymph nodes and lymph node aspirates. However, the molecular assays which are used to detect MRD are subject to certain (technical) problems which affect their sensitivity and specificity. In this paper we will present examples of molecular assays such as the plaque assay using p53 mutations and the E48 RT-PCR, and show their use for MRD detection in cervical lymph nodes. In addition, we will discuss the problems and pitfalls associated with these sensitive techniques.

Immunomagnetic separation for enrichment and sensitive detection of disseminated tumour cells in patients with head and neck SCC

Screening for malignant cells in the blood and bone marrow was introduced as a strategy for the improved detection of tumour spread and may predict the development of distant metastases. The sensitivity of these approaches depends on several factors, including the choice of antibody for immunocytochemistry (ICC) and the number of cells examined. In this study criteria have been defined for scoring cells reactive with a pan-cytokeratin antibody as tumour, by comparing immunostained cells in clinical samples obtained from head and neck cancer patients and a control group without epithelial malignancy. When leucocyte subfractions are prepared by density gradient separation (DGS) from central venous blood obtained from patients with advanced head and neck squamous cell carcinoma (SCC) and screened by ICC, epithelial tumour cells sediment preferentially with the mononuclear cells but may also be detected in the granulocyte (GC) fraction. Some cases were found to have more tumour cells in the GC fraction. Similar results were seen in model experiments. To increase the sensitivity of the ICC approach, the efficiency of positive immunomagnetic selection (IMS) using Dynabeads coated with an antibody recognizing the Ber-EP4 epitope has been compared with negative IMS using anti-CD45 Dynabeads. Tumour cells were recovered from bone marrow aspirates for 2/17 cases using the positive enrichment technique and for 11/17 patients following negative IMS. These findings justify prospective studies incorporating negative IMS to establish the prognostic significance of these disseminated tumour cells for this group of patients.

Detection of minimal disease in patients with solid tumors

The detection and elimination of minimal systemic disease in patients with solid tumors is one of the main current topics in clinical oncology. The present review focuses, therefore, on new diagnostic approaches to identify minimal disease in peripheral blood, bone marrow, and lymph nodes of patients with epithelial cancer as the major type of solid tumors in Western industrialized countries. These approaches may be used to improve tumor staging and monitoring of adjuvant therapies, as well as to detect tumor cell contamination in autologous stem cell grafts. Most investigators have developed either immunocytochemical assays with monoclonal antibodies to a variety of epithelial-specific cytoskeleton and membrane antigens or molecular methods based on the extensive amplification of a specific (c)DNA sequence by the polymerase-chain reaction (PCR). In immunocytochemical assays, antibodies to cytokeratins can be regarded as the most specific and sensitive probes to detect isolated epithelial tumor cells in bone marrow and blood. Molecular methods are based on the detection of either mutations in oncogenes and tumor suppressor genes (e.g., ki-ras and p53 genes) or the mRNA expression of tissue-specific and tumor-associated genes. mRNA species targeted in these assays encode cytokeratins, prostate-specific antigen, prostate-specific membrane antigen, carcinoembryonic antigen, and polymorphic-epithelial mucin. To introduce the available methods into clinical practice, standardized protocols need to be developed and validated in multi-center studies.