Discussion:
Differentiated thyroid cancer carries an excellent prognosis and the
development of metastasis is a rare event in everyday head and neck
oncology practice. In spite of the evolution of numerous protocols to
guide practice, metastases from DTC are treated heterogeneously across
treating centres. In our series, metastases were identified in 32 of 381
(8.4%) patients with DTC. The presentation of metastases from DTC is
insidious in many cases. In our series 19% (N=6) of patients underwent
treatment for conditions in the spine without being aware of primary
thyroid pathology. The fact that metastatic workup is not recommended by
all established guidelines and that thyroidectomy being a common ENT
procedure performed even in low resource non-specialty institutions
results in many patients to undergo limited surgeries like
hemithyroidectomy and who are subsequently diagnosed with metastases on
referral to specialized services after the initial surgery. We had 5
such patients in our series (16%) The incidence of bone metastasis was
4.5% (N=17) which is in concordance with published literature. Distant
metastases are associated with poor prognosis in differentiated thyroid
cancers. The most common site of bone metastasis in differentiated
thyroid cancers are vertebrae, ribs and hips. Tumour cell adhesive
molecules bind the tumour cells to marrow stromal cells and bone matrix
allowing them to grow and produce angiogenic and bone resorbing factors.
Metastasis of DTC have been treated with curative
intent1717.In a study
done by Isabelle et al, out of 43 patients who had undergone pulmonary
metastasectomy predominantly for follicular carcinoma, showed an
encouraging 10 year disease free survival of 84% in patients who
underwent complete resection. This significantly declined to 62% on
incomplete resection
(p=0.013)10.
In our study, the most common thyroid cancer histopathology was
papillary thyroid cancer followed by follicular cancer and poorly
differentiated thyroid cancers respectively.
There is uniformity across protocols on the recommendation of
radioactive iodine in patients with metastatic DTC in terms of a
survival advantage. In a study done on 228 patients, 71 received iodine
therapy with a cumulative dose of at least 600 mCi, This study
reiterated that there seemed to be a better prognosis with greater
cumulative doses of RAI but the disease specific mortality was 60% over
a 10 year follow up period when treated with higher cumulative
doses11, In our study,
all except one received radioactive iodine. The median dose of 400mCi is
in accordance with study published by Pitoia et al which showed that the
patient treated with a mean effective cumulative RAI dose of 457.3 ±
29.7 mCi I131 (300-600 mCi) had a good response to
treatment18.
It is imperative that young patients with metastatic DTC be warned of
the adverse effects of high dose radioiodine, most importantly
xerostomia, pulmonary fibrosis and infertility. The option of
cryopreservation of semen or oocytes may be offered to potential
recipients of high dose radioactive
iodine19.
The role of conventional EBRT has been well established in the
literature to allay pain, to improve neurological deficits and or to
prevent pathological fractures. Four patients in our series received
EBRT, all for the alleviation of pain. Studies show that radiation doses
vary from low risk microscopic disease (54 Gy), High risk (59.5 Gy) to
gross disease (63-70 Gy) to achieve local control
rates20. However, EBRT
has been found to show a higher rate of local progression and pain
relapse with long term follow
up21. In our research,
only four patients received EBRT to the metastatic site with a maximum
of 54 Gy and a minimum of 30 Gy.