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open access
6 JUN 2016
Ovary
There
are many histologic types of primary ovarian carcinomas, and each of
these is biologically unique with respect to histologic,
immunohistochemical, and molecular features and pathogenesis. High-grade
serous carcinoma is the most common ovarian malignancy and thus will be
the focus of discussion for this section. Recent research has
identified the precursor for this tumor as serous tubal intraepithelial
carcinoma (STIC), which originates in the mucosa of the distal
(fimbriated) end of the fallopian tube.
Terminology
STIC is the standardized designation for this form of intraepithelial neoplasia.[24, 25]
Lesions related to STIC are serous tubal intraepithelial lesions
(STILs) and “p53 signatures” (described below; see Molecular
Underpinnings). It should be noted that these latter 2 lesions are not
synonymous with STIC, and they are thought to precede the development of
STIC as part of its pathogenesis. STIL, which is an atypical mucosal
lesion intermediate between p53 signature and STIC, has also been
referred to by a variety of other descriptive terms.[26]
It also should be noted that the term p53 signature should be reserved
only for research studies and should not be used in the pathology
report.[21, 22]
Diagnostic Criteria
STIC is histologically characterized by significant nuclear atypia (Fig. 3).
Several studies; however, have used different criteria for
distinguishing STIC, atypical intermediate lesions, p53 signatures, and
normal mucosa from one another. Consequently, there are no standardized
criteria for these lesions, and the establishment of exact histologic
diagnostic criteria for STIC has been difficult, because the morphologic
spectrum of STIC is wide, and no 2 STICs appear to be exactly the same
because of various degrees of histologic overlap between STICs.
Variability of a diagnosis of STIC exists between pathologists, and
several studies have shown that the interobserver agreement among
pathologists based only on histologic features is inadequate.
For
these reasons and to establish working criteria for standardization
between pathologists for routine diagnosis and research, a diagnostic
algorithm was developed that combines histologic features with
coordinate immunohistochemical expression of p53 and Ki-67 (these
markers are used to assess mutant tumor protein 53 [p53] and the
proliferation index, respectively). Accordingly, STIC is diagnosed when
significant atypia is present in combination with abnormal p53
expression and a high Ki-67 index. Interobserver reproducibility studies
using this algorithmic approach have demonstrated that the agreement
for STIC between pathologists was improved to a substantial level (from κ
= 0.50 to κ = 0.67) compared with using only morphologic assessment and
that this algorithm can be reproducibly applied.[26]
Risk Factors
A subset of STICs is associated with breast cancer (BRCA)
germline mutations, whereas most STICs are sporadic. Other specific
risk factors have not yet been identified, although a diagnosis of STIC
before 40 years of age would be rare. The p53 signature, a putative
precursor of STIC, is significantly associated with lower parity[27]
(for additional information regarding the potential relation between
the p53 signature and STIC/invasive high-grade serous carcinoma, see
Vang et al).[25] However, the p53 signature does not appear to be associated with an increased risk of developing serous carcinoma.
Molecular Underpinnings
Abundant
histologic and molecular evidence that has emerged over roughly the
last 8 years strongly supports findings that the vast majority of
ovarian and peritoneal high-grade serous carcinomas originate in the
fallopian tube, specifically from an STIC, and thus implies that these
ovarian/peritoneal tumors are metastases.[25, 28]
It has been proposed that the p53 signature is the earliest step in the
pathogenesis of STIC. The p53 signature consists of short stretches of
tubal epithelium composed of cytologically benign, nonciliated
(secretory) cells with overexpression of p53 and a low Ki-67 labeling
index. However, the exact relation between p53 signatures and STIC is
unclear (for additional information regarding the potential relation
between the p53 signature and STIC/invasive high-grade serous carcinoma,
see Vang et al).[26] It has been demonstrated that nearly all STICs harbor TP53 mutations, and short telomeres and aneusomy for multiple chromosomes have also been observed. In women with BRCA germline mutations, it has been suggested that loss of the wild-type BRCA
allele is involved in tumor progression. STIL may represent a
transitional step in pathogenesis between the p53 signature and STIC.
Management, Limitations, and Caveats
STIC
may be recognized as an isolated finding in either 1) prophylactic
specimens from women with an increased risk of ovarian/tubal carcinoma
(ie, BRCA mutation carriers) or 2) routine specimens as part of
a gynecologic surgical procedure performed for benign indications in
women without a known history of breast/ovarian carcinoma or those not
known to be BRCA mutation carriers (ie, sporadic cases). For
such patients, the extent to which further clinical evaluation is needed
is unclear. Using chemotherapy in this situation has not been
preferred, but some patients in the literature have been treated in this
fashion. Also, a proportion of patients with STIC as an isolated
finding have had positive peritoneal cytology.
A
significant limitation to the complete understanding of the natural
history of STIC as an isolated finding is the availability of only a few
studies with limited numbers of cases and short follow-up. While one
study of isolated STIC observed no recurrences (median follow-up, 2.3
years),[29] a subset of patients in other studies subsequently developed recurrences as carcinoma from 3.6 to 4.0 years later.[30, 31] Furthermore, the outcome data on isolated STICs are based on BRCA germline mutation-associated cases. Because BRCA
germline mutation-associated ovarian high-grade serous carcinomas have
better survival than sporadic cases, it is possible that isolated
sporadic STICs may have a greater propensity for progression compared
with BRCA germline mutation-associated cases. Therefore,
because 1) STIC is the histologic and immunohistochemical counterpart to
endometrial serous intraepithelial carcinoma, 2) the latter can have
extrauterine disease in the absence of myometrial invasion, and 3) STIC
is typically located in the fimbriated end of the fallopian tube with
direct access to the peritoneal cavity, the prognosis for patients with
isolated sporadic STIC should be considered uncertain.
The
opportunistic salpingectomy has been recognized as a potential means of
preventing extrauterine high-grade serous carcinoma for women at
average risk in whom the fallopian tubes have been removed before STIC
can develop.[32]
Thus, the entire fallopian tubes are removed in women undergoing pelvic
surgery in instances in which an oophorectomy would not have been
performed (eg, tubal ligation and hysterectomy in premenopausal women).
Given that the ideal surgical candidate would be relatively young and
that the mean age of women with sporadic STIC is the early 60s, it will
likely be decades before future studies show the actual impact of the
opportunistic salpingectomy on the general population. However, recent
evidence suggests that this surgical procedure will be beneficial. In a
Swedish population-based study in which women underwent bilateral
salpingectomy, the risk for ovarian carcinoma was decreased by 65% (P = .004).[33]
If additional large studies with lengthy follow-up can confirm these
findings in women who undergo opportunistic salpingectomy, then this
form of prevention will be of enormous value to women, because current
screening modalities for detecting ovarian high-grade serous carcinoma
have been unsuccessful.
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