Signet ring appendix cancer is one of the rarest histologies of an already rare disease, accounting for roughly four percent of appendix cancer cases. For a long time, patients in this group had almost no published evidence to point to when they sat down with their oncology team. That gap is finally starting to close.

Over the past several years, a handful of multi-institutional studies and high-volume single-center series have started to fill in the picture for this subtype. The findings include some real and useful news. One of the most important is that signet ring features by themselves are no longer considered a reason to deny patients the surgery that has shown the best results, which is something some patients have been told in the past. There is genuinely useful information here for patients and the people who love them.

This is the first of three posts in our series on this subtype. Part 1 covers what the treatment evidence says today. Part 2 looks at what your pathology report actually says and which details matter most for your care. Part 3 covers the broader research framework now organizing around appendix cancer, why outcomes are still so hard to predict, and what patients can do to be part of changing that.

What signet ring cell carcinoma actually is

Signet ring cell carcinoma is defined by the appearance of the tumor cells under a microscope. The cells fill with mucin that pushes the nucleus to the edge, creating a shape that pathologists thought looked like a signet ring. The World Health Organization defines a tumor as signet ring cell carcinoma when more than half the tumor is made up of these cells.

Tumors with a smaller signet ring component, sometimes called signet ring features or tumors with signet cells, fall into a different category but behave more like signet ring carcinoma than like ordinary adenocarcinoma. That distinction matters, and we will come back to it.

Signet ring appendix cancers often present with peritoneal spread. These tumors are frequently associated with mucinous ascites and diffuse seeding across the peritoneal surface rather than a single large mass. This is why so many of these patients are diagnosed with peritoneal disease already present at the time of their first surgery, and why incidental finding during an appendectomy for what looked like appendicitis is one of the most common presenting stories in this subtype.

What the largest signet ring appendix cancer treatment studies tell us

The most directly relevant study published recently is a 2025 Mayo Clinic series. Researchers at Mayo’s Minnesota, Arizona, and Florida sites reviewed 84 patients with signet ring cell adenocarcinoma of the appendix treated between 1998 and 2024. The median age was 61. Most patients were women. Most tumors were high grade, and most patients had metastatic disease at diagnosis.

The five-year overall survival in patients who achieved complete cytoreduction was 25 percent. In this retrospective cohort, systemic chemotherapy was not associated with improved survival when added to cytoreductive surgery. Adding HIPEC to cytoreductive surgery showed a difference that was clinically meaningful, with 20 percent five-year survival in the CRS plus HIPEC group versus 5 percent with surgery alone (p=0.059, which did not reach statistical significance). The authors concluded that CRS with HIPEC was associated with the most favorable observed outcomes in their dataset, and that overall outcomes remain poor and new treatment approaches are needed.

The honest reading of this paper is not that CRS with HIPEC is a cure for signet ring appendix cancer. It is that surgery with HIPEC produced the best results in the dataset, and the gap between getting it and not getting it was meaningful. For patients who are candidates, that gap is worth knowing about.

The largest multi-institutional dataset is the US HIPEC Collaborative study, published in 2020 with results from twelve academic centers. Of 514 patients who underwent CRS with HIPEC for appendiceal adenocarcinoma, 125 had signet ring features, a quarter of the total. Overall survival was meaningfully worse for the signet ring group, with a median of 32 months compared to 91 months for non-signet ring patients.

But the authors made a point that has been important for the field. They concluded that while signet ring cells are a negative prognostic factor, the presence of signet ring cells should not by itself be a contraindication to CRS with HIPEC in patients with well or moderately differentiated tumors, negative lymph nodes, and disease where complete cytoreduction can be achieved.

The takeaway is that signet ring features affect prognosis, but signet ring appendix cancer patients can still benefit from CRS with HIPEC when their other features are favorable and a complete surgical clearance is possible. This is a meaningful finding because some surgeons and centers have historically considered signet ring features a reason not to offer CRS with HIPEC at all. The US HIPEC Collaborative data argues against that as a blanket rule, which has opened the door for patients who might otherwise have been turned away.

A third study worth understanding comes from Shamavonian and colleagues at St George Hospital in Sydney, Australia, published in the European Journal of Surgical Oncology in 2021. They looked at 255 patients with high-grade appendiceal cancer who underwent CRS with HIPEC and broke them into three groups based on how many signet ring cells were present in the tumor.

Patients with no signet ring cells had a median overall survival of 93.8 months. Patients with a low count of signet ring cells had a median survival of 58.2 months. Patients with a high count had a median survival of 23.7 months. The five-year overall survival rates were 60 percent, 35.5 percent, and 10 percent, respectively.

This is one of the most important findings in the signet ring literature, and it gets discussed less than it should. Signet ring cell carcinoma is not one disease. The amount of signet ring component in a tumor strongly predicts how the disease will behave. A patient whose pathology report mentions some signet ring cells is in a meaningfully different prognostic category from a patient whose tumor is more than fifty percent signet ring. For patients in the lower-percentage groups, the published outcomes are substantially better than the overall signet ring numbers patients often hear quoted. That is information worth having before any treatment conversation.

For more on why how patients are counted and classified in research has direct consequences for outcomes like these, see our earlier piece on why high-grade appendix cancer patients really need to be counted.

3 honest truths about signet ring appendix cancer treatment

Three things stand out consistently across these studies. Complete cytoreduction is the single most important treatment factor that has been consistently associated with better outcomes in this disease. When complete cytoreduction can be achieved at a high-volume center, it is the most evidence-supported path forward. When it cannot, the conversation becomes harder and more individual. Patients whose disease cannot be fully resected face a fundamentally different prognostic situation, and that should be discussed honestly rather than glossed over.

Systemic chemotherapy has not shown a consistent survival benefit across the major signet ring datasets. In the Mayo series, adding systemic therapy to surgery did not improve outcomes. In the US HIPEC Collaborative analysis, receipt of neoadjuvant or adjuvant chemotherapy did not improve overall survival in the signet ring group. This does not mean systemic chemotherapy is never used or never helpful for any individual patient. It means the evidence base for routinely giving it to signet ring patients is weaker than many patients have been led to believe, and the standard colorectal regimens being applied to appendix cancer patients were never designed for or tested in this histology. Recent work on molecular drivers like KRAS and PIK3CA, which we covered in our post on a new study about KRAS and PIK3CA in high-grade mucinous and signet ring cell carcinoma, is starting to point toward why this may be.

The signet ring appendix cancer research field is also paying more attention now than it has in years. Researchers are openly saying that current treatments need to improve, and they are actively working on it. Molecular profiling, immunotherapy candidates in select cases, and new translational research are all moving forward, and Parts 2 and 3 of this series cover where that work is heading.

Questions worth asking your team about signet ring appendix cancer

If you or someone you love has this diagnosis, a few questions are worth raising with the treatment team, drawn directly from what these studies establish.

How much of the tumor is signet ring cells, by percentage? This affects what the prognosis literature actually says about your specific situation, and many patients have never been told the number.

Has the case been reviewed at a high-volume peritoneal surface malignancy center, even if treatment is happening locally? Outcomes after CRS with HIPEC for appendiceal cancer vary meaningfully by center experience, and signet ring cases are exactly the situation where center experience matters most.

Is complete cytoreduction considered achievable based on imaging and surgical evaluation? If yes, the evidence supports having that conversation seriously at a high-volume center. If not, what is the goal of the proposed treatment, and what is the realistic expected outcome?

Has the tumor been tested for MSI status and mismatch repair? This question matters for a small but real subset of signet ring patients.

What this series will and will not do

We are not going to tell anyone what treatment to pursue. That conversation belongs between patients, their families, and their oncology team. What we can do is make sure the published evidence is sitting in front of patients in plain language, so that those conversations happen on a foundation of what is actually known rather than what is assumed.

Signet ring appendix cancer is one of the rarest histologies of an already rare cancer. The patients living with it deserve more attention than they have historically received, and the research community is finally starting to deliver it. Part 2 of this series covers what your pathology report actually says and why specific details matter for your care. Part 3 covers the broader research framework now organizing around appendix cancer and what patients can do to be part of moving it forward. There is more reason to pay attention now than there has been in years.

Why your data matters: the Appendicure registry

The studies in this post were possible because a handful of high-volume centers kept careful records on a small number of patients. That is how the field has worked for decades. Most signet ring appendix cancer patients are not treated at the Mayo Clinic, the academic centers in the US HIPEC Collaborative, or St George Hospital in Sydney. Their experiences, their pathology, and their outcomes sit scattered across health systems where no one is positioned to put the picture together.

That is the gap the Appendicure community data registry is built to close. By contributing your own information about diagnosis, treatment, and outcomes, you become part of a dataset that researchers can use to ask questions these studies could not. The kinds of questions a registry like this could help study include: How do outcomes compare for patients with twenty percent signet ring versus eighty percent? What happens to patients treated at community hospitals rather than referral centers? Which treatment sequences are working for the patients who are doing well, and what do they have in common?

These are questions a few retrospective studies, however carefully done, cannot answer alone. They require more patients, from more places, sharing their experience over time. Signet ring patients are the smallest subgroup in an already rare disease, which means every single contribution moves the needle more than it would in a more common cancer. If you have signet ring appendix cancer, or care for someone who does, your data is exactly what the next generation of research needs.

Contribute to the Appendicure registry →

Read next

Part 2: Signet Ring Appendix Cancer Pathology: What Your Report Actually Says

Why high-grade appendix cancer patients really need to be counted

What a new study tells us about KRAS and PIK3CA in high-grade mucinous and signet ring cell carcinoma

References

Hor and colleagues. Effectiveness of treatment modalities for signet ring cell adenocarcinoma of the appendix. American Journal of Surgery, 2025.

Levinsky and colleagues. Should we be doing cytoreductive surgery with HIPEC for signet ring cell appendiceal adenocarcinoma? A study from the US HIPEC Collaborative. Journal of Gastrointestinal Surgery, 2020.

Shamavonian and colleagues. Impact of signet ring cells on overall survival in peritoneal disseminated appendix cancer treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy. European Journal of Surgical Oncology, 2021.