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Original Studies |
Endocrine Laboratory, Department of Medicine and Therapeutics and Department of Surgery, St. Vincents Hospital and University College Dublin, Dublin 4, Ireland
Address all correspondence and requests for reprints to: Dr. P. P. A. Smyth, Endocrine Laboratory, Department of Medicine and Therapeutics, Woodview, University College Dublin, Dublin 4, Ireland. E-mail: ppa.smyth{at}ucd.ie
| Abstract |
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0.3 U/mL were associated with a significantly better
disease-free [relative risk (RR) = 1.84, P <
0.05] and overall survival (RR = 3.46, P <
0.02), compared with those who were TPO.Ab-negative. Better outcome
associated with higher TPO.Ab titres was confined to those who had
thyroid volumes within the intermediate range (10.118.8 mL) and did
not further enhance the good outcome recorded when volumes were
10.0 mL or > 18.8 mL. Multivariate survival analysis showed that
both TPO.Ab and thyroid volume were independently associated with
prognosis in breast carcinoma and that RRs for disease-free survival
were of a similar order of magnitude to well-established prognostic
indices such as axillary nodal status or tumor size. These findings
supply evidence that manifestations of thyroid autoimmunity are
associated with a beneficial effect on disease outcome in breast
carcinoma and provide the strongest evidence to date of a biological
link between breast carcinoma and thyroid disease. | Introduction |
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The objective of the present study was to investigate TPO.Ab, using a direct RIA, in sera from patients who had either breast carcinoma or benign breast disease (BBD), with or without coincident thyroid enlargement, and to examine whether the presence of TPO.Ab contributed to the outcome in breast carcinoma. \.
| Subjects and Methods |
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The breast carcinoma group consisted of 356 women, 3281 yr old (median, 57), with a histological diagnosis of invasive breast carcinoma, who were attending a single specialist clinic. Patients who had undergone therapy for thyroid disease were excluded from the study. Only those patients whose breast carcinoma was first diagnosed during the period of the study were included. Survival analysis was restricted to a group of 142 women in whom a first potentially curable invasive breast carcinoma was diagnosed during the period of this study and whose thyroid volume and TPO.Ab status were determined during potentially curative treatment for their breast carcinoma. Clinical, pathological, and follow-up data were recorded prospectively, using a computerized database. The median time between diagnosis and thyroid volume/serum TPO.Ab estimation was 5 months.
BBD
This group consisted of 122 patients, 1650 yr old (median, 36) with clinical or histological evidence of fibrocystic breast disease or fibroadenoma.
Controls
Control groups (A and B) consisted of women recruited from the same geographical area who had no clinical evidence of breast disease and who had a similar age distribution to those of the breast carcinoma and BBD patients, respectively [group A: age range, 3284 yr (median 55); group B: age range, 1845 yr (median 34)].
The study populations (patients and controls) were restricted to persons who had no history of overt thyroid disease.
Thyroid function tests
Serum TT4 and TSH were estimated by immunoassay using an IMX analyzer (Abbott laboratories, Diagnostic Division, Ireland Ltd). The TSH assay was second generation, with a functional sensitivity of 0.05 mU/L.
Serum TPO. Ab were measured using a highly sensitive direct RIA (RSR, Cardiff, UK). TPO. Ab titres were recorded as U/mL Medical Research Council Standard 66/387. The upper limit of the reference range was 0.3 U/mL (8).
Thyroid volume was measured by ultrasound using a 7.5-mHz linear transducer. The volume of each lobe was calculated using the formula: width x depth x length x 0.479 (9). Volumes more than 18.0 mL were termed: enlarged (10).
Statistics
Statistical analysis was performed using the
-square,
Mann-Whitney U and Krushkal-Wallis tests. The relationship between
TPO.Ab and patient outcome was studied using the recursive partitioning
technique (11), the Mantel-Haensel log-rank test (12), and the Cox
proportional hazards model (13). Survival curves were constructed using
the Kaplan-Meier method (14).
| Results |
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18.0 mL)
or enlarged (>18.0 mL) thyroid volumes, is shown in Table 2
18.0 mL (30.8%, P >
0.05). In contrast, the prevalence of TPO.Ab more than 0.3 U/mL in BBD
was significantly greater (50.0%) when thyroid volume was more than
18.0 mL than when it was
18.0 mL (22.6%, P <
0.05). Comparison of TPO.Ab titres, between breast carcinoma and BBD
groups, showed that breast carcinoma patients were no more likely to
have higher TPO.Ab titres than those with BBD (P >
0.05).
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The effect of TPO.Ab titres on survival in the 142 patients with breast
carcinoma using this threshold is shown in Fig. 2
. As shown in Fig. 2a
, the 2 survival
curves diverge with TPO.Ab
0.3 U/mL (upper curve)
being associated with better disease-free survival, compared with
values less than 0.3 U/mL [73%, compared with 56% at 5 yr, relative
risk (RR) = 1.84, P = 0.047]. Similarly, in Fig. 2b
, overall survival was significantly better when TPO.Ab were
0.3
U/mL (upper curve). Five-year survival was 91% when TPO.Ab
were
0.3 U/mL, compared with 80% (TPO.Ab < 0.3 U/mL;
RR = 3.46, P = 0.0160).
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10.0 mL were
assigned a thyroid volume score of 0, patients with thyroid volumes
more than 18.8 mL were assigned a thyroid volume score of 1, and
patients with intermediate thyroid volumes (10.118.8 mL) were given a
score of 2. Similarly, patients with TPO.Ab
0.3 U/mL were given
a TPO.Ab score of 0, whereas those with volumes less than 0.3 U/mL were
given a score of 1. In this analysis, both thyroid volume and TPO.Ab
status emerged as significant independent prognostic factors for
disease-free survival (RR being 2.210 and 2.315, respectively;
P = 0.003 and 0.011). The comparable RRs for axillary
nodal status and tumor size were 2.336 and 1.829; P =
0.003 and 0.001, respectively. The RR for overall survival associated
with TPO.Ab less than 0.3 U/mL (3.424) was similar to that associated
with being axillary node-positive (3.031), P = 0.043
and 0.026, respectively. In the current study, tumor size and thyroid
volume were not significantly associated with disease outcome, as
measured by overall survival in multivariate analysis, and are
therefore not included in the results presented in the table.
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10.0 mL was unaffected by the level of TPO.Ab
(RR = 1.18, P = 0.892). Survival curves were
superimposed. However, it should be noted that numbers of patients with
volumes in this category were relatively low (8 TPO.Ab-negative and 14
TPO.Ab-positive). Similarly, as shown in the lower graph
(Fig. 3c
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0.3 U/mL was associated
with a significantly better disease-free survival (RR = 2.41,
P = 0.019). Survival at 5 yr was 65%, compared with
40% when TPO.Ab was less than 0.3 U/mL. Overall survival curves for
breast carcinoma patients, grouped on the basis of both TPO.Ab titre
and thyroid volume, are shown in Fig. 4
0.3 U/mL, respectively. The
level of TPO.Ab was not significantly associated with survival when
thyroid volumes were less than 10.0 mL (RR = 1.57,
P = 0.747) or more than 18.8 mL (RR = 1.81,
P = 0.601). In contrast, when thyroid volume was in the
intermediate range (10.018.8 mL), as shown in Fig. 4b
0.3 U/mL was associated with a significantly better
survival, compared with breast carcinoma patients whose TPO.Ab were
less than 0.3 U/mL (RR = 14.14, P = 0.0004). In
this intermediate thyroid volume category, the 5-yr overall survival of
55%, when TPO.Ab was less than 0.3 U/mL, increased to 95% when TPO.Ab
was
0.3 U/mL; and the difference increased with increasing
time. | Discussion |
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The finding of higher serum TSH values, even within the reference range, together with the presence of TPO.Ab, may indicate susceptibility to future hypothyroidism (15). The tendency towards thyroid hypofunction, evident in the skewed distribution of serum TSH values in breast carcinoma patients associated with TPO.Ab positivity, is consistent with previous reports showing an association between thyroid disease and breast carcinoma, in which hypothyroidism was the most frequently observed finding (16, 17).
The findings in the present study confirm recent reports of higher TPO.Ab positivity in women with breast carcinoma (6, 7). They also demonstrate an increased prevalence of TPO.Ab positivity in BBD and are in agreement with the earlier finding of a higher prevalence of Hashimotos thyroiditis in Japanese women with breast carcinoma (3).
TPO.Ab positivity was associated with a better disease outcome in the
142 patients with breast carcinoma who had TPO.Ab values
0.3
U/mL, compared with those with values less than 0.3 U/mL. The potential
importance of the association between TPO.Ab, thyroid volume, and
outcome in breast carcinoma was emphasized by the finding that the
magnitude of the prognostic effect for disease-free survival of thyroid
volume and TPO.Ab (RR = 2.21 and 2.31, respectively) was
comparable to that for axillary nodal status and tumor size, often
regarded as the most important prognostic characteristic of women with
breast carcinoma. Similarly, nodal status and TPO.Ab had comparable RRs
for overall survival (3.03 and 3.42, respectively). Because the
prognostic significance of both thyroid volume and TPO.Ab were
independent of and additional to the information provided by
established risk factors, they therefore cannot be attributed to an
association with such factors.
Thus, both the presence of TPO.Ab positivity, as shown in this study,
and of smaller (
10.0 mL) and larger (>18.8 mL) thyroid volumes
previously demonstrated (2) are associated with a better outcome in
breast carcinoma. Indirect support for these findings was provided by
reports that suggested that patients with breast carcinoma and
coincidental thyroid disease may have a good outcome (18, 19, 20). The
better outcome associated with higher TPO.Ab titres was not additive to
that associated with smaller or larger thyroid volumes. This finding is
supported by the absence of an association between TPO.Ab positivity
and increased thyroid volume in patients with breast carcinoma
investigated in this study.
The mechanisms through which TPO.Ab positivity or reduced/enlarged thyroid volumes might influence breast carcinoma progression remain a matter of conjecture. Because the association of TPO.Ab positivity with improved outcome was only observed when thyroid volume was in the intermediate range (10.118.8 mL), it would seem that thyroidal involvement, whether in terms of volume or antibody positivity, was effected via different pathways. TPO.Ab positivity has been shown to be an important factor in antibody-dependent cell cytotoxicity in the thyroid (21), although no such evidence exists for the breast. A factor that can result in either a smaller or larger thyroid gland is the presence of thyrotrophin receptor antibodies (TRAb), which have been shown to both stimulate and impede thyroidal growth (22, 23, 24). Although extrathyroidal expression of thyrotrophin receptors has been recently demonstrated (25, 26), they have not, as yet, been located in mammary tissues. Whether these antibodies could interact with receptors on breast tumors is unknown but is the subject of further study. Although we do not yet have a definitive explanation for our findings, they do provide the strongest evidence to date of a biological link between breast carcinoma and thyroid disease.
| Acknowledgments |
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| Footnotes |
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Received March 5, 1998.
Revised May 4, 1998.
Accepted May 12, 1998.
| References |
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