NEW YORK (GenomeWeb) – Researchers from the University of Michigan have used next-generation sequencing to characterize genetic changes that occur in serous tubal intraepithelial carcinomas, lesions that are often precursors to high-grade serous carcinomas.
As reported online in JAMA Oncology today, Michigan's Kathleen Cho and her colleagues performed next-generation sequencing on samples obtained from a set of four women to identify genetic changes in serous tubal intraepithelial carcinomas. From this, they not only found that TP53 mutations are early driving events for high-grade serous carcinomas, but also that some serous tubal intraepithelial carcinomas may actually be metastases rather than precursor lesions.
"We demonstrate that targeted NGS can identify genetic alterations in minute lesions, such as [tubal intraepithelial carcinomas], and confirm TP53 mutations as early driving events for HGSC," Cho and her colleagues wrote in their paper.
The researchers obtained tubal intraepithelial carcinomas samples from four women undergoing total abdominal hysterectomy/bilateral salpingo-oophorectomy due to malignant gynecological neoplasms. Two of the patients also had high-grade serous carcinomas and the other two had uterine endometrioid carcinomas.
After manual microdissection to isolate tubal intraepithelial carcinomas and matched carcinoma samples, the researchers performed targeted next-generation sequencing using the Ion Torrent PGM sequencer on between 5 and 20 nanograms of sample. Using a custom AmpliSeq panel, they targeted some 135 cancer-related genes.
They reached a median depth of coverage of 432x and mapped a median 1.1 million reads. Some 85 percent of target bases had 100x coverage.
All four patients, the researchers reported, had somatic TP53 mutations in their tubal lesions. This, they noted, is consistent with previous reports suggesting that TP53 mutations occur early in HGSC pathogenesis.
There was evidence, the researchers added, of a clonal association between the TICs and the primary serous ovarian carcinomas in the two patients with those tumors.
Both of these patients also had germline BRCA1 and BRCA2 mutations, the researchers reported. STICs, they added, are often found in the fallopian tubes of women with germline BRCA mutations and high-grade serous carcinomas. Some 5 percent of women undergoing prophylactic total abdominal hysterectomy/bilateral salingo-oophorectomy to reduce their risk of high-grade serous carcinomas have lesions, they noted.
However, the lesions in the third patient were genetically heterogeneous, Cho and her colleagues found. For instance, the TIC harbored a single T53 mutation while the uterine endometrioid carcinoma had somatic mutations in MTOR, PTEN, KRAS, PIK3CA, and ATM. This, they said, suggests that the two lesions are genetically distinct and developed through independent neoplastic processes in the fallopian tube and uterus. This patient, they added, did not have predisposing BRCA1, BRCA2, or MSH2 germline variants.
Additionally, the tubal lesion in the fourth patient had somatic PTEN and CTNNB1 mutations as well as a TP53 mutation, though the matched uterine endometrioid carcinoma only exhibited the PTEN and CTNNB1 mutations. Immunohistochemical staining further found a clonal staining pattern in the TIC and wild-type staining in the primary tumor. Additional staining found that both tumor types in this patient expressed PAX8, but not WT-1.
Gauging by Ki-67 staining, the researchers said that the TIC had a proliferative index of about 40 percent while the primary tumor had between 20 percent and 30 percent Ki-67 staining. This, the researchers added, indicates that the tubal lesion in this patient is actually a micrometastasis from the uterine endometroid carcinoma rather than a STIC.
"These findings highlight that although STICs may be precursors to HGSC, not all high-grade TICs are of tubal origin," the researchers said.
Additionally, they noted that as their pilot study found that targeted sequencing is possible on small epithelia lesions, "more comprehensive sequencing may be useful in identifying possible lesions driving progression and potential biomarkers to assist with early detection or minimal residual disease monitoring."