The Li-Fraumeni syndrome (LFS): a model for the initiation of p53 signatures in the distal Fallopian tube

A candidate early precursor to pelvic serous cancer, the 'p53 signature', is commonly found in the benign mucosa of the distal Fallopian tube and harbours p53 mutations and evidence of DNA damage. We examined tubes from women with pre-existing (germ-line) mutations in p53 [Li-Fraumeni syndrome (LFS)] for evidence of this precursor. Fallopian tubes from two cases of LFS were immunostained for p53, Ki-67 (proliferation) and H2AX (DNA damage response) and analysed for p53 mutations by laser capture microdissection (LCM) and p53 genomic sequencing (exons 2-11). A common single nucleotide repeat (snp) in exon 3 (rs1042522) and deletion sequencing chromatograms in exon 4 were examined in combination to estimate LOH in both LFS tubes and advanced serous carcinomas from the general population. LFS tubal epithelium contained abundant (10-20 per section) p53 signatures with evidence of DNA damage and low proliferative activity. Six of 11 LFS microdissected p53 signatures (55%) and 15 of 21 serous carcinomas (71%) revealed LOH at the p53 locus, relative to background epithelium. The LFS model confirms prior observations that the distal Fallopian tube is particularly prone to focal epithelial p53 gene inactivation-p53 mutation and LOH-in the absence of malignancy or increased epithelial proliferation. The fact that the LFS is not associated with ovarian cancers is consistent with the concept that loss of p53 function must be accompanied by at least one more genotoxic event (including BRCA1/2 functional inactivation) to produce the malignant phenotype. This is in keeping with a general model of carcinogenesis, in which different and often independent risk factors operate at multiple points in the serous carcinogenic spectrum.

Primary ex vivo cultures of human fallopian tube epithelium as a model for serous ovarian carcinogenesis

Recent studies suggest that some serous ovarian carcinomas (SOCs) arise from the fallopian tube (FT) epithelium rather than the ovarian surface epithelium. This hypothesis places emphasis on the FT secretory epithelial cell as a cell-of-origin. Herein, we report the development of a novel ex vivo primary human FT epithelium culture system that faithfully recapitulates the in vivo epithelium, as shown by morphological, ultrastructural and immunophenotypic analyses. Mass spectrometry-based proteomics reveal that these cultures secrete proteins previously identified as biomarkers for ovarian cancer. We also use this culture system to study the response of the FT epithelium to genotoxic stress and find that the secretory cells exhibit a distinct response to DNA damage when compared with neighboring ciliated cells. The secretory cells show a limited ability to resolve the damage over time, potentially leaving them more susceptible to accumulation of additional mutagenic injury. This divergent response is confirmed with in situ studies using tissue samples, further supporting the use of this ex vivo culture system to investigate FT epithelial pathobiology. We anticipate that this novel culture system will facilitate the study of SOC pathogenesis, and propose that similar culture systems could be developed for other organ site-specific epithelia.

Epidemiologic correlates of ovarian cortical inclusion cysts (CICs) support a dual precursor pathway to pelvic epithelial cancer

OBJECTIVE

Many ovarian carcinomas are presumed to arise within ovarian cortical inclusion cysts (CICs). This study examined the frequency of ovarian CICs in relation to epidemiologic risk factors in women with BRCA1 and BRCA2 (BRCA+) mutations.

METHODS

BRCA+ women who underwent risk-reducing bilateral salpingo-oophorectomy were studied (n=74). Fifteen demographic variables (e.g., age at time of surgery, age at first birth, age at menopause, body mass index (BMI), gravidity) from a review of the medical records and three pathologic variables (cystic and atretic follicles, corpora lutea) were recorded. Statistical associations were made using T-test or Chi Square analysis and logistic regression analysis for p-trend.

RESULTS

Women whose ovaries contained 7 for more CICs were older at first birth (p=0.034), surgery (p=0.059), menopause (p=0.046) and had a higher BMI (p=0.034) than those with <7 CICs. Regression analysis revealed a significant association between CICs and increasing BMI (p=0.01).

CONCLUSIONS

CICs correlate with greater body mass index, similar to low-grade serous and endometrioid tumors and in contrast to high-grade serous carcinoma and its putative precursor in the fallopian tube. A model is presented for ovarian and tubal pathways to pelvic cancer that are linked to different microscopic precursors with distinct epidemiologic correlates.

Evidence for a latent precursor (p53 signature) that may precede serous endometrial intraepithelial carcinoma

Both serous intraepithelial carcinoma and endometrial glandular dysplasia are associated with uterine serous carcinoma. Recently a candidate serous cancer precursor containing p53 mutations (p53 signature) was described in the fallopian tube. We analyzed normal and neoplastic endometrium for a similar entity. In total 10 endometrial polyps involved by intraepithelial and/or invasive carcinoma and 137 benign polyps were studied. All were stained for p53 and MIB-1. A subset of p53 signatures and carcinomas were analyzed for gamma-H2AX and p53 mutations. p53 signatures were identified in 7 of 10 cases intraepithelial carcinoma and were multicentric in 2. In one case, the signature was in continuity with intraepithelial carcinoma. Of 137 benign polyps (4%), 6 contained p53 signatures. The MIB-1 fraction in most signatures was less than 5%, and ranged from 50 to 90% in carcinomas. DNA damage (gamma-H2AX) was demonstrated in both p53 signatures and adjacent carcinomas but not in benign polyps. Shared identical p53 mutations were found in paired signatures and carcinomas in two of three cases analyzed, including one case with multiple signatures. In one, a coexistent invasive serous cancer was not found to contain a p53 mutation. In a third, a p53 signature and an invasive cancer harbored two different p53 mutations. This is the first description of p53 signatures adjacent to carcinoma, suggesting a role for this entity in the genesis of serous malignancy. The significance of p53 signatures in benign conditions (polyps) remains to be determined. The role of the p53 signature in early serous neoplasia is discussed.

Precursors to pelvic serous carcinoma and their clinical implications

Pelvic serous carcinoma has traditionally been viewed as a rapidly evolving malignancy, due principally to its late stage at diagnosis and tendency for poor outcome, both in the endometrium and the upper genital tract. Recently, studies of women with BRCA1 or BRCA2 mutations (BRCA+) undergoing risk reducing salpingo-oophorectomy have highlighted the distal fallopian tube as a common (80%) site of tumor origin and additional studies of unselected women with pelvic serous carcinoma have demonstrated that serous tubal intraepithelial carcinoma may precede a significant percentage of these tumors. This review examines the serous carcinogenic spectrum in the fallopian tube, highlighting recent evidence that these tumors may follow a defined precursor that has been present for a prolonged interval. The data supporting a candidate precursor, the implications of these findings for early detection and prevention of pelvic serous carcinoma and the caveats, are discussed.

Intercepting pelvic cancer in the distal fallopian tube: theories and realities

The pathogenesis of high-grade serous carcinoma of the ovary has come into sharper focus as closer attention has been paid to the earlier phases of this disease. The study of patients with BRCA mutation has been of particular value, in as much as the examination of prophylactic salpingo-oophorectomies will reveal an early cancer in approximately 5% of individuals. Recently studies have shown that about 80% of these early carcinomas originate in the distal fallopian tube. This review summarizes the recent data supporting the distal fallopian tube as an important site for serous carcinogenesis, stressing both the presence of a novel precursor (the p53 signature) and the application of this model to all women irrespective of BRCA status. The challenges and unmet needs unmasked by this paradigm shift in ovarian cancer research are discussed.

Squamous morules are functionally inert elements of premalignant endometrial neoplasia

Squamous morules are a common component of premalignant glandular lesions that are followed by glandular, rather than squamous, carcinomas. We tested the hypothesis that the appearance of glands associated with morules predicts cancer risk, and undertook molecular testing to determine the clonal and hormonal response properties of admixed squamous and glandular elements. A total of 66 patients with squamous morules in an index endometrial biopsy had follow-up clinical data (average follow-up: interval 31 months, 2.5 biopsies) showing development of carcinoma in 11% (7/66) of cases. The histological appearance of morule-associated glands in the index biopsy was significantly associated with this clinical outcome, with the majority (71%, 5/7) of cancer occurrences following an overtly premalignant lesion (endometrial intraepithelial neoplasia) with squamous morules. Eight endometrial intraepithelial neoplasias with squamous morules were examined by immunohistochemistry for estrogen and progesterone receptors and mitotic activity (Ki-67 antigen percent stained). Glandular components had abundant estrogen and progesterone receptors, and high levels of mitotic activity in all cases. In sharp contrast, all squamous morules were devoid of sex hormone receptors and had undetectable or extremely low-proliferation rates. When mutated, the same specific PTEN mutation was detected in squamous and glandular elements, indicating that both are of common lineage. The clinical and laboratory data are consistent with a model of morule biology in which squamous morules are a hormonally incompetent subpopulation of endometrial glandular lesions. Isolated morules might result from artifactual displacement from their native glandular context, or selective hormonally induced regression of the glandular but not squamous components over time. Subsequent cancer risk, as promoted by estrogens, is greatest when the glandular component has the appearance of endometrial intraepithelial neoplasia. Even isolated morules should be carefully followed, however, to exclude a coexisting undersampled, or occult, glandular lesion.

Serous tubal intraepithelial carcinoma: its potential role in primary peritoneal serous carcinoma and serous cancer prevention

PURPOSE

A diagnosis of primary peritoneal serous carcinoma (PPSC) requires exclusion of a source in other reproductive organs. Serous tubal intraepithelial carcinoma (STIC; stage 0) has been described in asymptomatic women with BRCA mutations and linked to a serous cancer precursor in the fimbria. This study examined the frequency of STIC in PPSC and its clinical outcome in BRCA-positive women.

PATIENTS AND METHODS

Presence or absence of STIC was recorded in consecutive cases meeting the 2001 WHO criteria for PPSC, including 26 patients with nonuniform sampling of the fallopian tubes (group 1) and 19 patients with complete tubal examination (group 2; sectioning and extensively examining the fimbriated end, or SEE-FIM protocol). In selected cases, STIC or its putative precursor and the peritoneal tumor were analyzed for p53 mutations (exons 1 to 11). Outcome of STIC was ascertained by literature review.

RESULT

Thirteen (50%) of 26 PPSCs in group 1 involved the endosalpinx, with nine STICs (35%). Fifteen (79%) of 19 cases in group 2 contained endosalpingeal involvement, with nine STICs (47%). STIC was typically fimbrial and unifocal, with variable invasion of the tubal wall. In five of five cases, the peritoneal and tubal lesion shared an identical p53 mutation. Of 10 reported STICs in BRCA-positive women, all patients were without disease on follow-up.

CONCLUSION

The fimbria is the source of nearly one half of PPSCs, suggesting serous malignancy originates in the tubal mucosa but grows preferentially at a remote peritoneal site. The generally low risk of recurrence in stage 0 (STIC) disease further underscores STIC as a possible target for early serous cancer detection and prevention.

Risk factors for a serous cancer precursor ("p53 signature") in women with inherited BRCA mutations

OBJECTIVES

Pelvic (ovarian) serous carcinomas frequently contain p53 mutations. Recently, a candidate serous cancer precursor (the p53 signature) with p53 mutations and other features in common with serous cancer has been discovered in distal fallopian tube mucosa. This study examined the relationship of putative ovarian cancer risk factors with the presence of p53 signatures in women with BRCA mutations (BRCA+).

METHODS

Fallopian tubes from 75 BRCA+ women were immunostained for p53 signatures and correlated with age at first childbirth, parity, oral contraceptive use, body mass index (BMI), and BRCA subtype (1 or 2). Statistical analysis was performed with the T-test or Chi-square analysis and logistic regression adjusting for age and parity.

RESULTS

Thirty-eight percent of the tubes contained p53 signatures, which were significantly associated with older age at first childbirth (mean 30.8 vs. 28.4 years; p=0.04) and lower parity (mean 1.4 vs. 2.2; p=0.01) in univariate analyses. The unadjusted odds ratios were 3.8 (p-trend=0.04) for first childbirth>/=30 years versus <30 and 0.2 (p-trend=0.01) for parity >/= 3 versus nulliparous women. After adjusting for age and parity, the trend for age at first childbirth became non-significant (adjusted odds ratio 3.5; p-trend=0.15), while that for parity remained significant (adjusted odds ratio 0.2; p-trend 0.02).

CONCLUSIONS

The p53 signature is significantly associated with lower parity and possibly higher age at first childbirth, further linking this entity to serous cancer via risk factors associated with ovulation. The p53 signature merits consideration as a surrogate marker for serous cancer risk.

Tubal and ovarian pathways to pelvic epithelial cancer: a pathological perspective

Prolongation of ovarian epithelial cancer survival depends on early detection or improved responses to chemotherapy. Gains in either have been modest at best. Understanding the diverse pathogenesis of this disease is critical to early intervention or prevention. This review addresses six important variables, including (i) cell of origin, (ii) site of origin, (iii) initial genotoxic events, (iv) risks imposed by hereditary and other promoting conditions, (v) subsequent factors that promote different patterns of metastatic spread, and (vi) prospects for intervention. This review proposes two distinct pathways to pelvic epithelial cancer. The first initiates in ovarian surface epithelium (OSE), Mullerian inclusions or endometriosis in the ovary. The second arises from the endosalpinx and encompasses a subset of serous carcinomas. The serous carcinogenic sequence in the distal fallopian tube is described and contrasted with lower grade serous tumors based on tumour location, earliest genetic change and ability (or lack of) to undergo terminal (ciliated) differentiation. Ultimately, a clear understanding of tumour origin and the mechanism(s) leading to the earliest phases of the serous and endometrioid carcinogenic sequences may hold the greatest promise for designing prevention strategies and/or developing new therapies.

Recent advances in the understanding of the pathogenesis of serous carcinoma: the concept of low- and high-grade disease and the role of the fallopian tube

In the past 50 years, the concept of serous ovarian cancer has been progressively refined, with the distinction of the borderline serous tumour, identification of a smaller subset of well-differentiated serous malignancies and, recently, closer attention to the pathogenesis of high-grade serous malignancies. High-grade serous carcinoma, traditionally presumed to arise within Müllerian inclusion cysts of the ovarian surface, cortex and peritoneum, has recently been linked to the distal fallopian tube. This review addresses the disparate forms of serous neoplasia, which reflect both different genetic abnormalities and stages of differentiation of Müllerian epithelium. The significance of these different origins is addressed in the context of ovarian cancer prevention.

Pathophysiology of placenta creta: the role of decidua and extravillous trophoblast

Placenta creta is associated with massive postpartum hemorrhage and commonly leads to emergency hysterectomy. While the exact pathogenesis of placenta creta is unknown, proposed hypotheses include a primary deficiency of decidua, abnormal maternal vascular remodeling, excessive trophoblastic invasion, or a combination thereof. To assess these changes in placenta creta, we retrospectively reviewed 49 cases of gravid hysterectomy, 38 with and 11 without the diagnosis of creta, gathered clinical data, and evaluated histopathology of extravillous trophoblast. Specifically, we evaluated maternal vessels for remodeling by endovascular trophoblast, as well as the morphology and depth of invasion of interstitial trophoblast at the implantation site. Compared to controls, cases with creta had decreased proportion of remodeled vessels, with many vessels displaying partial physiologic change. Cases with creta also demonstrated vascular remodeling deeper in the myometrium; however, vascular remodeling of large outer myometrial vessels was only demonstrated in increta and percreta cases, and was absent in both non-creta and accreta. As previously reported, interstitial trophoblast invaded the uterine wall to a significantly greater depth in placenta creta; however, there was no significant difference between creta subtypes. Finally, Ki-67 staining was rarely observed in extravillous trophoblast, except in the trophoblast columns of first trimester creta cases. We, therefore, conclude that the pathogenesis of placenta creta is multi-dimensional, involving increased, but incomplete trophoblast invasion in a background of absent decidua. We further propose that placenta increta and percreta are not due to a further invasion of extravillous trophoblast in the uterine wall, rather they likely arise secondary to dehiscence of a scar, leading to the presence of chorionic villi deep within the uterine wall, and thus give extravillous trophoblast greater access to the deep myometrium.

A candidate precursor to pelvic serous cancer (p53 signature) and its prevalence in ovaries and fallopian tubes from women with BRCA mutations

BACKGROUND

Early serous carcinomas predominate in the fimbria of women with BRCA mutations (BRCA+). An entity in non-neoplastic mucosa sharing several properties of early serous carcinomas--the "p53 signature"--has been described in the distal fallopian tube and proposed as a precursor to serous carcinomas. This study compared the prevalence of p53 signatures in ovarian cortical inclusion cysts (CICs) and fallopian tubes from BRCA+ women and explored their relationship.

DESIGN

All tissues from 75 completely excised ovaries and tubes obtained during prophylactic surgery were studied by conventional microscopy, immunostaining for p53, and in selected cases, gamma-H2AX (DNA damage). P53 signatures were defined as 12 or more consecutive p53-positive secretory cell nuclei. Their prevalence in fallopian tubes and CICs was recorded, compared to an existing database of consecutive women without a suspicion of BRCA+ or ovarian cancer, and correlated with the number of CICs.

RESULTS

Tubal p53 signatures were detected in 29 of 75 cases (38%); 20 of 30 (66%) signatures examined were gamma-H2AX-positive. One ovary contained a small gamma-H2AX negative p53 signature on the ovarian surface; no p53 signatures were identified in CICs. The prevalence of BRCA+ p53 tubal signatures was similar to that of women with unknown BRCA status (38 v 33%). Presence of p53 signatures did not correlate with number of CICs.

CONCLUSIONS

p53 signatures were common in the fallopian tubes of BRCA+ women, were not identified in CICs, and did not correlate with the latter. The tubal p53 signature merits serious consideration as an important early event in serous carcinogenesis in BRCA+ women.

Expression patterns of MITF during human cutaneous embryogenesis: evidence for bulge epithelial expression and persistence of dermal melanoblasts

The mechanisms whereby melanocytes populate the epidermis and developing hair follicles during embryogenesis are incompletely understood. Recent evidence implicates an intermediate mesenchymal stage in this evolutionary process in which HMB-45-positive melanocyte precursors ('melanoblasts') exist both in intradermal as well as intraepithelial and intrafollicular compartments. The melanocyte master transcriptional regulator, microphthalmia transcription factor (MITF), identifies mature melanocytes as well as melanocyte precursor stem cells that reside in the bulge region of the hair follicle.

METHODS

To better define the use of MITF expression in the evaluation of melanocyte ontogeny, human embryonic and fetal skin samples (n = 28) at 6-24 weeks gestation were studied immunohistochemically for expression of MITF and Mart-1. Adjacent step sections were evaluated to correlate staining patterns with cell localization in the intraepidermal, intrafollicular and intradermal compartments.

RESULTS

At 6-8 weeks, MITF and Mart-1-positive cells were primarily intradermal with only rare positive cells in the epidermis. By 12-13 weeks, most of these cells had migrated into the epidermis, predominantly the suprabasal layers. Between 15-17 weeks, these cells localized to the basal layer and colonized developing hair follicles. Rare intradermal MITF and Mart-1 positive cells were found as late as week 20. At 18-24 weeks, MITF and Mart-1 positive cells were identified in the outer root sheath, bulge, and follicular bulge epithelium, in addition to the epidermis. Unexpectedly, weak but diffuse nuclear MITF expression was also present in the keratinocytes of the bulge area.

CONCLUSIONS

The in situ migratory fate of MITF/Mart-1-expressing cells in fetal skin involves a well-defined progression from intradermal to intraepidermal to intrafollicular localization. Occasional intradermal melanocytes may persist after the intraepithelial stages are completed, a finding of potential significance to melanocytic proliferations that may arise de novo within the dermis. Because MITF may play a role in stem cell maintenance, the presence of MITF in bulge epithelial cells suggests that it may be a novel marker for follicular stem cells of both epithelial and melanocytic lineage.

Using the rate of positive high-risk HPV test results for ASC-US together with the ASC-US/SIL ratio in evaluating the performance of cytopathologists

We reviewed our experience with 2 indicators of cytopathologist performance: the relative frequency of the interpretations atypical squamous cells of undetermined significance (ASC-US) and squamous intraepithelial lesion (SIL) and the frequency of positive test results for high-risk human papillomavirus (HR-HPV) DNA associated with a cytologic interpretation of ASC-US. Data derived for 9 cytopathologists were reviewed. ASC-US/SIL ranged from 0.99 to 4.02 (mean, 1.77) in 2005 and from 0.82 to 3.68 (mean, 1.81) in 2006. The HR-HPV+ rate for ASC-US ranged from 31.5% to 54.6% for individual cytopathologists (mean, 46.1%) in 2005 and from 29.6% to 61.8% (mean, 45.8%) in 2006. Combined data from both years showed only a slight negative correlation for these 2 variables. Both indicators together provide useful feedback to cytopathologists. We provide a working schema for interpreting perturbations in these indicators to assist in improving the quality of gynecologic cytology interpretations.

Primary fallopian tube malignancies in BRCA-positive women undergoing surgery for ovarian cancer risk reduction

PURPOSE

To review the frequency and location of malignancies detected after prophylactic salpingo-oophorectomy in women with BRCA mutations.

METHODS

Medical records and pathology findings were reviewed from BRCA-positive women undergoing prophylactic surgery for ovarian cancer risk reduction who underwent complete examination of the adnexa. Patients undergoing this procedure between January 1999 and January 2007 were identified.

RESULTS

From January 1999 to January 2007, 122 BRCA-positive patients underwent prophylactic surgery in the Division of Gynecologic Oncology at Brigham and Women's Hospital. The median age was 46.5 years (range, 33 to 76 years). Seven (5.7%) were found to have an early malignancy in the upper genital tract and all patients were age > or = 44 years at diagnosis. Of seven consecutive cancers culled between January 1999 and January 2007, all (100%) originated in the fimbrial or ampullary region of the tube; six had an early (intraepithelial) component. Two were associated with surface implants on the ovary and two required repeated sectioning to detect microscopic carcinomas in the fimbria.

CONCLUSION

The distal fallopian tube seems to be the dominant site of origin for early malignancies detected in approximately 6% of women undergoing ovarian cancer risk-reduction surgery. The greatest proportion of serous cancer risk in BRCA mutation-positive women should be assigned to the fimbria rather than the ovary, and future clinical and research protocols should employ thorough examination of the fimbria, including multiple sections from each tissue block, to maximize detection of early malignancies in this population.

Biomarker-assisted diagnosis of ovarian, cervical and pulmonary small cell carcinomas: the role of TTF-1, WT-1 and HPV analysis

AIMS

Small cell carcinoma of the ovary, hypercalcaemic-type (SCCOH) is morphologically similar to small cell carcinomas from other sites. The aims of this study were to (i) determine if a biomarker panel would distinguish small cell carcinomas of the ovary, cervix (SCCCx) and lung (SCCLu) and (ii) potentially determine the histogenesis of SCCOH.

METHODS AND RESULTS

Nine ovarian small cell carcinomas (seven hypercalcaemic type; two pulmonary type), eight SCCCx and 22 SCCLu were immunostained for thyroid transcription factor (TTF)-1, WT-1, p16, cKIT and OCT3/4; a subset of cases were tested for human papillomavirus (HPV). WT-1 was diffusely positive in 6/7 SSCOH versus two of 33 other small cell carcinomas (P <or= 0.001). TTF-1 was diffusely positive in 20/22 SCCLu and 1/8 SCCCx, and negative in all SCCOH. p16 and cKIT demonstrated variable patterns of immunoreactivity in all cases. HPV was identified in 5/6 SCCCx; SCCOH and SCCLu were negative for HPV.

CONCLUSIONS

Combined staining with WT-1 and TTF-1 will distinguish SCCOH from SCCLu and SCCCx with a sensitivity of 86% and specificity of 97%. HPV is specific for tumours of cervical origin, but p16 immunohistochemistry is not useful for this purpose. The presence of diffuse WT-1 supports a Müllerian origin for SCCOH, whereas the absence of cKIT and OCT3/4 argues against a germ cell origin.

BRAF in Papillary Thyroid Carcinoma of Ovary (Struma Ovarii)

BACKGROUND

Malignant struma ovarii (MSO) are rare tumors that arise from ectopic thyroid tissue in the ovary, benign struma ovarii (BSO). Most MSO are histologically classified as papillary thyroid carcinomas (PTC). Oncogenic activation of BRAF (35% to 69%), RAS (10%), or RET (5% to 30%) is common in PTC, and the mutations correlate with tumor subtype, patient age, and clinical behavior. In this study, we explored the possible role of these genes in the development of BSO and MSO.

DESIGN

Six paraffin-embedded cases of MSO with histopathologic features of PTC (4 follicular variants, 1 classic, and 1 metastasis of a classic) and 9 BSO were identified. BRAF, NRAS, and KRAS mutations were evaluated using a combination of polymerase chain reaction, denaturing high performance liquid chromatography, and automated sequencing. RET alterations were screened by fluorescence in situ hybridization with multicolor probes. Corresponding benign tissues were evaluated when available.

RESULTS

BRAF mutations were present in 4 of 6 MSO and none of 9 BSO. The BRAF mutations included V600E (2 cases), K601E, and a novel deletion/substitution TV599-600M. Neither MSO nor BSO contained alterations in NRAS, KRAS, or RET.

CONCLUSIONS

The development of MSOs with PTC features is associated with BRAF mutations of the type commonly observed in PTC, suggesting a common pathogenesis for all PTCs regardless of location. In contrast, mutations in the RET/RAS/RAF pathway are not found in BSO. The prognostic significance of BRAF mutation status in MSO remains to be determined.

p63 Is essential for the proliferative potential of stem cells in stratified epithelia

The distinguishing feature of adult stem cells is their extraordinary capacity to divide prior to the onset of senescence. While stratified epithelia such as skin, prostate, and breast are highly regenerative and account disproportionately for human cancers, genes essential for the proliferative capacity of their stem cells remain unknown. Here we analyze p63, a gene whose deletion in mice results in the catastrophic loss of all stratified epithelia. We demonstrate that p63 is strongly expressed in epithelial cells with high clonogenic and proliferative capacity and that stem cells lacking p63 undergo a premature proliferative rundown. Additionally, we show that p63 is dispensable for both the commitment and differentiation of these stem cells during tissue morphogenesis. Together, these data identify p63 as a key, lineage-specific determinant of the proliferative capacity in stem cells of stratified epithelia.

A unifying concept of trophoblastic differentiation and malignancy defined by biomarker expression

Several trophoblast phenotypes, including cytotrophoblast, syncytiotrophoblast, and extravillous trophoblast, emerge during gestation. To clarify the lineage relationship between these subtypes, we profiled p63 localization in developing and term placental tissue, as well as in trophoblastic tumors, using antibodies specific to full-length (TAp63) and one against all p63 isoforms (TAp63 and DeltaNp63). Localization of p63 was compared with that of biomarkers of proliferation and trophoblastic differentiation, including mib-1, inhibin, and MelCAM. In early gestation, p63 was localized principally to villous cytotrophoblast after contact with the villous mesenchyme, absent in the trophoblast columns, and early implantation trophoblast. In the maturing placenta, intraplacental perivillous fibrin correlated with the emergence of a p63-positive "transitional" (vacuolated) extravillous trophoblast from cytotrophoblast, which differentiated further into a "mature" p63-negative extravillous trophoblast. The same lineage pathway emerged from entrapped villi on the chorionic membrane. Virtually all p63 immunopositivity was attributed to dominant-negative p63. The immunophenotypic patterns seen in the immature and mature placenta permit the resolution of all trophoblastic phenotypes within 3 lineage pathways of cytotrophoblast differentiation, including cytotrophoblast-to-trophoblast column/implantation site, cytotrophoblast-to-syncytiotrophoblast, and cytotrophoblast-to-mature extravillous trophoblast. In the latter pathway, a transitional (vacuolated) p63-positive extravillous trophoblast emerges from and links cytotrophoblast to mature extravillous trophoblast in intraplacental fibrin, chorionic membrane, and basal plate. The placental trophoblast is thus resolved within this continuum of differentiation. Terms such as transitional and mature extravillous trophoblast are proposed to reflect the differentiation phases of this unique epithelium. p63 staining patterns in trophoblastic tumors reflect timing of neoplastic transformation during trophoblastic differentiation.