|Year : 2017 | Volume
| Issue : 2 | Page : 111-114
Micrometastasis: Neglected enough!
Prathyusha Chavva, Devaraju Devaiah, Vijeev Vasudevan, Manjunath Venkatappa
Department of Oral Medicine Diagnosis and Radiology, Krishnadevaraya College of Dental Sciences and Hospital, Bengaluru, Karnataka, India
|Date of Submission||11-May-2016|
|Date of Acceptance||22-Oct-2017|
|Date of Web Publication||9-Nov-2017|
Department of Oral Medicine Diagnosis and Radiology, Krishnadevaraya College of Dental Sciences and Hospital, Bengaluru - 562 157, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Oral cancer, being the sixth most common cancer in the world, accounts for approximately 13% of deaths worldwide. Metastasis to the lymph nodes is one of the major prognostic factor for oral cancer. Micrometastasis are microscopic deposits of malignant cells lodged in lymph nodes. Tumor recurrence usually reflects the presence of such deposits which cannot be detected initially by conventional methods. Early screening of such cells using immunological and molecular markers would help in better staging of the primary tumor followed by prompt treatment, thus reducing tumor relapse. Therefore, the concept of micrometastasis has resulted in a paradigm shift in the staging of epithelial tumors and the overall understanding of the malignant process.
Keywords: Molecular detection, oral field cancerization, sentinel lymph node, tumor staging
|How to cite this article:|
Chavva P, Devaiah D, Vasudevan V, Venkatappa M. Micrometastasis: Neglected enough!. J Indian Acad Oral Med Radiol 2017;29:111-4
| Introduction|| |
Oral cancer is a serious public health problem accounting for over 7.6 million deaths annually across the globe. In India, the incidence of oral cancer is 73.6 per 100,000 population. The overall mortality rate for intraoral cancer remains high at approximately 50%, even with modern medical services available. Five-year survival rates of oral cancer are not improving despite the progression of multidisciplinary treatment because distant metastasis is the major cause of death in individuals suffering from cancer. Metastasis, the spread of tumors, is one of the important characteristics of malignancy, which has a definite bearing on prognosis. Micrometastasis is a microscopic deposit of malignant cells distinct from the primary lesions., Lymph node metastasis decreases survival by 50%, and spread beyond the lymph node capsule further decreases survival. Tumor recurrence and failure of treatment usually reflects the presence of occult malignant cells, which are not detected by diagnostic procedures. At present, there are various ways of identification of micrometastasis, i.e. histopathological serial sectioning, molecular methods of detection by the use of polymerase chain reaction (PCR) assays, detection of molecular markers of specific mutations,, keratin mRNA (mRNA) detection, etc. The present review discusses the pathology of micrometastasis, methods of detection of lymph node micrometastasis, and the significance of detecting circulating tumor cells and bone marrow deposits in head and neck cancer.
| Micrometastasis|| |
De Masceral et al. defined micrometastasis as metastatic deposits which measured less than 0.5 mm in diameter. Tumor deposits within the lymph nodes were classified and staged according to the revised guidelines which were set by the UICC (International Union Against Cancer): metastasis ≥2 mm, micrometastasis >0.2 and <2 mm, and isolated tumor cells ≤0.2 mm. The detection of micrometastasis has resulted in an “upstaging of tumors” and the incorporation of micrometastatic disease into the TNM staging system. The UICC/TNM protocols have been established for head and neck sentinel nodes.
Generic TNM coding for sentinel nodes:
- pNX (sn) Sentinel lymph node could not be assessed
- pN0 (sn) No sentinel node metastasis
- pN1(sn) Sentinel node metastasis.
Sentinel nodes with micrometastasis only are identified by (mi):
- pN1 (sn) (mi) Single ipsilateral node with micrometastasis
- pN2 (sn) (mi) Multiple ipsilateral nodes with micrometastasis.
Sentinel nodes with isolated tumor cells are coded separately for morphological and nonmorphological techniques such as PCR or flow cytometry:
- pN0 (i-)(sn) No sentinel lymph node metastasis histologically, negative morphological findings for isolated tumor cells (ITC)
- pN0 (i+)(sn) No sentinel lymph node metastasis histologically, positive morphological findings for isolated tumor cells (ITC)
- pN0 (mol-)(sn) No sentinel lymph node metastasis histologically, negative nonmorphological findings for isolated tumor cells (ITC)
- pN0 (mol+)(sn) No sentinel lymph node metastasis histologically, positive nonmorphological findings for isolated tumor cells (ITC).
This has been evaluated in the study conducted by Atula et al. to study the micrometastasis in sentinel lymph nodes in oral and oropharyngeal squamous cell carcinoma. Regional metastasis to the lymph nodes had a definite bearing on prognosis. Any proposal to treat micrometastasis must first clarify which detection methods should be used to identify these malignant cells.
| Detection of Lymph Node Micrometastasis|| |
Oro and oropharyngeal cancers spread through lymphatic pathways to the cervical lymph nodes. Thus, nodal status determines prognosis in epithelial malignancies and governs the indications for adjuvant therapy. Early detection of micrometastatic disease could identify the patients who are most likely to benefit from adjuvant therapy. The various methods of detection have been described below.
Sentinel lymph node biopsy
Lymphatic afferents from a primary tumor drain into a single focus, termed sentinel node, before drainage into regional lymphatic basin. It localizes the first draining node of a tumor site for more accurate histological staging., The procedure consists of injecting a radiolabelled colloid around the primary tumor that drains into the first echelon lymph nodes, which can be detected by the use of gamma probes.
Advantages of sentinel node biopsy
- Detailed pathological examination for micrometastatic deposits are possible because of small tissue volume
- Reduces the morbidity of nodal acquisition and may obviate formal lymph node dissection in patients with negative sentinel nodes
- Accurate identification of metastatic cells are possible because of rigorous examinations of multiple sections through the nodes.
The Sentinel Node European Trail (SENT) pathology protocol  has advised evaluation of the sentinel lymph node biopsy that has the ability to detect all micrometastatic deposits with certainty. It was used in oral cancer by Blide et al. who demonstrated upstaging from 4 to 22% using the SENT protocol.
Epithelial cells in the lymph nodes may be detected by the use of specific anti-cytokeratin (CK) antibodies against cytokeratin proteins, which form an essential constituent of the cytoskeleton of the epithelium, serving as reliable markers for identifying micrometastasis. This technique has been shown to be far superior to hematoxylin and eosin (H and E) staining alone. Because CKs are highly expressed in epithelial tumors, CK19 and CK20 have been evaluated frequently. Germani et al. conducted a study to identify Membrane Type-1 Matrix Metalloproteinase (MT1-MMP) by immunohistochemical analysis in oral SCC and concluded that MT1-MMP positivity is suggestive of aggressive tumor types, evidenced by the presence of micrometastasis.
Molecular assays are 500 times more sensitive than standard histopathological techniques. Initially, PCR-based assays using p53 gene for detection of micrometastasis in head and neck cancer was carried out by Brenan et al. They found that only 5 of 33 nodes examined by light microscopy had evidence of metastasis, whereas it increased to 11 of 33 nodes by the use of molecular studies.
A second method of identification used was reverse transcriptase (RT)-PCR, in which RNA is prepared and reverse-transcribed to complementary DNA, which is amplified with primers for gene of interest. Hamakawa et al. studied the expression of keratin mRNA for detecting micrometastasis in cervical lymph nodes of oral cancer. Of 166 histologically tumor free lymph nodes of oral cancer, 24 (14.4%) were found tumor positive by the detection of K13 RT-PCR. Squamous Cell Carcinoma Antigen mRNA (SCCA mRNA) has been used to detect micrometastasis in cervical lymph nodes for head and neck cancer using nested PCR. Hamakawa et al. reported detection of micrometastasis in 18.7% of cases, suggesting that SCCA mRNA can be a specific marker for detection of micrometastasis.
Detection of micrometastasis in bone marrow and blood
Recurrence in oral cancer is because of the presence of tumor cells, which are disseminated and detected in the hematopoietic cell compartment. Many protocols currently employed for detection of these isolated tumor cells rely on examination of monocytes obtained from peripheral or central venous blood or bone marrow. The methods commonly used for detection are immunocytochemistry, flow cytometry, and RT-PCR. It has been of poor prognostic significance in breast, lung, and colorectal cancer, and little has been known about its role in head and neck cancer. Wollenberg et al. conducted a study in 108 patients with SCC of the head and neck region and identified 41 patients with bone marrow micrometastasis.
Thus, if molecular or immunohistologic information is taken into account when staging is performed, a significant percentage of cases found to have micrometastasis would be upstaged; and taken together with other clinicopathological features of the tumor, this information might influence the decision regarding the need for postoperative radiotherapy, and possibly prevent treatment failure in the neck. The concept of oral field cancerization (OFC) was first described by Slaughter et al. in 1953, which highlighted that there are large areas of the head and neck that get exposed to the carcinogen making it more susceptible for development of many foci of malignant transformation. van Oijen MG et al. in 2000, explained the concept of OFC on the basis of two types of migration  i.e.,
- Migration of tumor cells, example saliva, i.e., micrometastasis
- Intraepithelial migration of the progeny of the initially transformed cells [Figure 1].
|Figure 1: Mechanisms of oral field cancerization showing (a) independent events, (b) migration of tumor cells, and (c) intraepithelial migration of progenitor cells (Jayam R. Oral field cancerizaton: A review. J Indian Aca Oral Med Radiol 2010;22:201-5)|
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As a result of proteolysis, cells from the primary tumor invade the blood vessels and migrate to a distant site where they adhere to the walls of the capillaries causing invasion of a new organ. Such cells are not detectable by conventional procedures and can survive for a longer time. The “micrometastatic concept” lays focus on the potential capacity of the tumor cells to evade immune surveillance, invade vascular channels, and develop into macroscopic disease [Figure 2].
|Figure 2: Metastasis of tumor cells (Pantel K, Cote RJ, Fodstad Ø. Detection and clinical importance of micrometastatic disease. J Natl Cancer Inst 1999;91:1113-24)|
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Majority of tumor cells undergo apoptosis, but a few which manage to survive become lodged in nodes depending on the local environment and host immune response. Tumor deposits ≤2 mm survive because of diffusion of nutrients from surrounding tissue, but >2 mm require neo-angiogenesis for tumor growth. If this does not occur, tumor remains dormant. A proportion of such deposits may acquire mutations overtime and ultimately proliferate to produce a new tumor focus. These provide a niche for evolution of tumor cells with a phenotype conducive to development of distant metastasis. Thus, early detection of micrometastasis has offered valuable insight into the behaviour of malignant cells, improving staging accuracy followed by prompt treatment enhancing survival of the patient.
| Conclusion|| |
Although progress has been made in clinical oncology, the presence of minimal residual cancer in the form of micrometastasis has limited improvement in lethality rates. A question arises as to whether these cells are dormant representation of residual disease or do they exist in a dynamic state despite host immunity. As lymph node micrometastasis has been shown to be an important adverse prognostic factor in oral and oropharyngeal SCC, the very least that can be done is to incorporate detection of micrometastasis into future clinical trials and management strategies!
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]