Histology of the thyroid parenchyma in papillary carcinomas shows an increased incidence of focal lymphocytic thyroiditis, usually considered to be an effect rather than a cause. In view of the frequency of occult papillary microcarcinomas, it has been suggested that these might be in situ carcinomas that are sometimes promoted to invasive tumours by unknown endogenous factors or by environmental factors, or by both.
See also:
ΓÇó Histology of Papillary Carcinoma of the Thyroid
