Low FAM46C Predictive of Inferior Survival Following Curative Resection for Gastric Adenocarcinoma

Low FAM46C expression appears to be an independent prognostic factor of inferior disease survival among patients with gastric adenocarcinoma who are undergoing curative intent surgical resection, according to findings that were presented at the 2022 International Gastric Cancer Congress.

The distant disease-specific survival was 58.0% for the overall patient population. Of 158 patients, the median FAM46C tumor over normal ratio was 0.24. Log FAM46C expression was reduced in gastric cancer compared with paired normal mucosa for 94% of patients. Additionally, high FAM46C expression (n = 79), which was defined as T/NM greater than or equal to the median, was associated with a superior survival. Investigators reported a 3-year disease specific survival rate of 75% in patients who were FAM46C high compared with 56% for patients who were FAM46C low (P = .02).

“We showed that low FAM46C is independently associated with inferior disease-specific survival and suppresses gastric cancer cell migration and invasion in in vitro experiments. This suppression was partially from inhibition of PLK4. Finally, low FAM46C expression is associated with differential ion channel expression,” according to Ning Fu, MD, of the University of Ottawa who presented the data on behalf of Shelly Luu, MD, PhD, a general surgery resident at the University of Toronto..

Investigators launched the research with 2 goals: to interrogate FAM46C status in resected gastric cancer specimens and find correlations with clinical outcomes, and to investigate FAM46C as a potential oncosuppressor. Investigators identified a total of 256 curative intent gastric adenocarcinoma resections from 2001 to 2017. In total, 29% of patients had inadequate or missing tissue blocks and 71% had their RNA extracted. Among those who had their RNA extracted, 23 patients had insufficient or poor-quality RNA, leading to 158 patients being included in the final study cohort.

Patients had a median age of 70 years (range, 21-92) and 62% of patients were male.

Fifty-nine percent of patients had distal and 61% had intestinal type disease. In terms of staging, patients had AJCC stage I (22%), II (35%), and stage III disease (42%). In total, 44% of patients received adjuvant treatment. Patients had a median follow up of 32 months, during which 37% of patients developed disease recurrence.

Findings from the multivariable analysis indicated that low FAM46C expression was independently associated with inferior disease-specific survival along with proximal tumor location and stage III disease.

Fu also spoke to the potential of FAM46C as a tumor suppressor for patients with gastric cancer.

“Previous work from our lab has highlighted the role of PLK4 in promoting breast cancer cell migration and invasion,” he explained. “Given that FAM46C suppresses PLK4, we are interested in seeing whether FAM46C [can] suppress gastric cancer cell migration and invasion by inhibiting PLK4.”

Findings from the scratch wound assay indicated that knocking down FAM46C increased migration, suggesting that endogenous FAM46C was successful in suppressing invasion. Similar findings were uncovered using the Transwell invasion assay.

“Prior to being described as an inhibitor of PLK4, FAM46C had not been shown to regulate cell motility, so we’re interested in seeing whether FAM46C’s ability to suppress migration is solely dependent on PLK4 inhibition,” Fu continued.

Investigators designed an assay to assess FAM46C PLK4 in gastric cancer cell migration in which PLK4 could be inhibited in the context of a FAM46C knock down. Centrinone-B, a specific inhibitor of PLK4 activity that has been shown to impair breast cancer cell migration, was used. It was observed that Centrinone-B also impaired gastric cancer cell migration.

In AGS gastric cancer cells with no PLK4 activity due to treatment with Centrinone-B, knocking down FAM46C increased migration in gastric cancer cells relative to the control group, albeit to a lesser degree than PLK4 functional cells. This may suggest that the ability of FAM46C to suppress gastric cancer cell migration may be partially reliant on PLK4 inhibition, Fu explained.

“Finally, we are interested in identifying other genes and pathways that may involve FAM46C in gastric cancer that are PLK4 independent,” Fu explained. “In order to do this, we performed RNA sequencing on 21 paired patient gastric tissues. We stratified the cohort into high vs low FAM46C expression using a median tumor over normal FAM46C expression, and we performed differential gene analysis of tumor vs normal mucosa for each of these subgroups separately.”

RNA sequencing revealed differentially expressed genes between FAM46C high and low tumors. When looking at functional clustering of GO terms, none achieved significance in the high FAM46C expression group, although expression some ion channel pathways were enriched in the low FAM46C group. This suggests FAM46C-low tumors had significant dysregulation of ion channel expression.

Reference

Luu S, Fu N, Kazazian K, et al. Fam46c/Tent5c expression predicts post-resection survival and suppresses gastric cancer progression. 2022 International Gastric Cancer Congress; March 6-9, 2022; Houston, TX.