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Tonsilar cancr that has spread to lymph nodes are not called metastatic cancer because they are regional lymph nodes.
If his lymph nodes show extracapsular spread then chances of disease recurrence is very high. Ideally he should have received radiation
together with chemotherapy
Most important thing to decrease chance of recurrence is to smoking
and drinking which are main risk factors for throat cancer
.Most common symptoms of relaps are recurrence of lymph node swelling, ulcer in throat, pain ,difficulty in taking food or breating