Two biomarkers are heritable DNA changes while three are somatic DNA alterations

By looking out for five biomarkers, it is now possible to tell in advance if a person with oral cancer of the gum and cheek has lymph node metastasis even before surgery is undertaken, a study has found. The ability to correctly predict absence/presence of lymph node metastasis in oral cancer patients is 80-90% based on the five biomarkers, a team led by Partha Majumder from the National Institute of Biomedical Genomics, Kalyani, West Bengal, has found.

As a result, an oral cancer patient can be spared of a neck dissection to investigate if the cancer has spread to the lymph nodes in case the five biomarkers are absent. Lymph node dissection increases morbidity. However, if the patient tests positive for even one biomarker then an aggressive treatment would be required. An oral cancer patient with cancer spread to the lymph node has a 50% lower chance of survival for five years or more compared with patients in whom it has not spread to the lymph node.

Hypothesis

In oral cancer patients, the cancer cells tend to commonly spread to the lymph node in the neck. But not all oral cancer patients have the tendency for the cancer to spread to other organs (metastasis). “We posited that oral cancer patients who have lymph node metastasis possess DNA alterations in specific genes that provide cancer cells the ability to spread. These DNA alterations are different from those that cause the primary cancer, and these alterations arise independent of the stage of cancer,” says Prof. Majumder.

So in some patients, the cancer would have spread to the lymph node even at an early stage of oral cancer, while in some patients with advanced (T4 stage) oral cancer, the cancer would not have spread.

To find out what determines lymph node metastasis in oral cancer patients, the team studied two groups of patients — those with lymph node metastasis and those with advanced oral cancer but without lymph node metastasis. Totally, 72 patients belonging to these two groups were studied by a team led by Dr. Rajiv Sarin, Director of Advanced Centre for Treatment, Research and Education in Cancer (ACTREC), Tata Memorial Centre, Mumbai and co-author of the paper.

Five genomic biomarkers

The team found that lymph node metastasis was associated with five genomic biomarkers. The results were published in International Journal of Cancer.

There are five genomic features or biomarkers of lymph node metastasis in oral cancer patients. Two of these are rare, heritable DNA changes in BRCA2 and FAT1 genes. The remaining three are non-heritable (somatic) DNA alterations. The somatic DNA alterations can occur in genes belonging to three different pathways — mitotic G2/M cell-cycle pathway, homologous recombination (HR) and non-homologous end joining (NHEJ) DNA-repair pathways.

Heritable DNA changes

The protein product of FAT1 gene functions as an adhesion molecule that keeps the cells together. In the case of cancer, cellular adhesion property is sometimes lost and the cells tend to spread. “Our finding that rare alterations in FAT1 are found in metastatic oral cancer is comprehensible, but new,” Prof. Majumder says. “Also, our finding that some rare alterations in BRCA2, which cause breast cancer, can also cause metastasis is novel.”

A cell duplicates to produce two daughter cells. Many genes are involved in this cell-cycle pathway, called mitotic G2/M pathway. If DNA of one or more genes of this pathway is altered, then many adverse cellular events take place. Most importantly, chromosomes become unstable and abnormal chromosomal changes occur, eventually leading to metastasis. “We have mapped DNA alterations in genes that belong to the mitotic G2/M pathway in oral cancer patients and have found that altered genes of this pathway promote lymph node metastasis,” says Dr. Nidhan Biswas, the first author of the paper.

Two pathways

When two major pathways — homologous recombination and non-homologous end joining — of DNA damage repair machinery gets perturbed, cells tend to behave abnormally. “We have found that DNA alterations in oral cancer patients that can be mapped to these pathways promote lymph node metastasis,” Prof. Majumder says. “So, metastasis in oral cancer is not promoted by a unique event.”

“The results have to be validated in a larger patient cohort,” says Dr. Sarin. “We have enrolled many patients to validate the results of this study. Besides TMC, the validation has to be done at other centres in India too.”

“We have found that a patient who presents without lymph node metastasis survives longer disease-free after standard treatment for oral cancer than one with metastasis of the lymph node. Therein lies the importance of our work,” says Prof. Majumder.