Abstract 5641: The viral load in nasopharyngeal swabs rather than the serum viral load during the course of primary radiotherapy can predict the likelihood of local recurrence in patients with nasopharyngeal carcinoma
Authors: Tsang Ngan M. 
Published: February 2011

PURPOSE: The presence of EBV latent membrane protein-1 (LMP-1) gene in nasopharyngeal swabs indicates the presence of nasopharyngeal carcinoma (NPC) tumor cells. This study was undertaken to investigate whether the viral load in nasopharyngeal (NP) swabs after a cumulative dose of 4,000 cGy during radiotherapy (RT) was inversely associated with NPC local control.

METHODS AND MATERIALS: During April 2000 and June 2007, there were 77 non-disseminated NPC patients receiving serial examinations of NP swabbing with the detection of LMP-1 during the course of RT. The median number of NP swabs performed was 5 among the studied patients. EBV DNA in NP swabs was quantified using real-time quantitative PCR. LMP-1 regression was defined as minimal viral load which was represented by being lower than 1,000 copies per 200 μg DNA in the specimen obtained via NP swab. The primary outcome was freedom from local recurrence, which represented local tumor control. In addition, 36 cases had at least 2 serum stocks during the course of RT as well. The median number of serum stocks obtained was 4 in this patient subgroup. If available, serial serum EBV viral loads were also checked to evaluate whether they were correlated with the viral loads in NP swabs.

RESULTS: At the time of analyzing the data, there were 18 cases (23%) developing local recurrence after completion of RT. Reviewing the viral load in NP swabs after a cumulative dose of 4,000 cGy during RT, there were 14 locally recurrent cases whose viral loads were greater than 1,000 copies/200 μg DNA in the specimens of NP swabs. On the other hand, among the 59 patients who have not experienced local recurrence at the time of current analysis, 28 non-recurrent NPC patients had a viral load greater than 1,000 copies/200 μg DNA during the corresponding period. The NPC patients would have a significantly higher likelihood of experiencing local recurrence if the viral loads in their NP swabs are still greater than 1,000 copies/200 μg DNA after a cumulative dose of 4,000 cGy during the course of definitive RT (chi-square test, p = 0.031). Paradoxically, it was observed in our study that serum EBV viral loads failed to decline rapidly during the course of RT as the viral loads in NP swabs did. In the majority of the studied patients, the serum viral loads tended to be stationary during RT. Focusing on the patients with an increasing level of viral load during primary RT, neither distant metastases nor local recurrence have occurred among them by the time of current analysis.

CONCLUSION: After a cumulative total dose of 4,000 cGy during RT, the NPC patients have a statistically greater risk of developing local recurrence if the viral loads in NP swabs were greater than 1,000 copies/200 μg DNA. Conversely, the alteration of serum viral loads during RT fails to predict the probability of local recurrence after definitive RT.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5641.