Metastasis in thyroid gland come most commonly from carcinoma of
The above-mentioned book is solely dedicated to surgery and diseases of thyroid & parathyroid gland.

It writes -
"Metastatic disease to the thyroid may occur as a consequence of direct extension from upper aerodigestive malignancies, i.e., squamous cell Ca, or by hematogenous spread. Evidence at autopsy has demonstrated upto 20% of patients exhibiting distant metastasis to the thyroid gland from breast, lung, kidney, & melanoma skin most commonly."
Testis
Prostate
Breast
Lungs