Sunitinib-Induced Elevation of Mean Corpuscular Volume (MCV)—Exploring Its Possible Clinical Relevance in Cancer Patients

Round 1

Reviewer 1 Report

The treatment landscape for several tumor types has changed dramatically over the last decade; for example, as regards renal cell carcinoma, the standard of care has shifted from monotherapy, typically a multi-targeted tyrosine kinase inhibitor (TKI), to combination therapies including immune checkpoint inhibitors (ICI).

Thus, the study addresses a timely topic.

Some changes are necessary in my opinion:

• Introduction section: although the authors correctly included important papers in this setting, we believe the background of sunitinib in medical oncology should be better explained and some papers should be cited within the introduction ( PMID: 34265504), only for a matter of consistency. We think it might be useful to introduce the topic of this interesting study.
• Methods and Statistical Analysis: nothing to add.
• Discussion section: Very interesting and timely discussion. Of note, the authors should expand the Discussion section, including a more personal perspective to reflect on. For example, they could answer the following questions – in order to facilitate the understanding of this complex topic to readers: what potential does this study hold? What are the knowledge gaps and how do researchers tackle them? How do you see this area unfolding in the next 5 years? We think it would be extremely interesting for the readers.

However, we think the authors should be acknowledged for their work. In fact, they correctly addressed an important topic, the methods sound good and their discussion is well balanced.

One additional little flaw: the authors could better explain the limitations of their work, in the last part of the Discussion.

We believe this article is suitable for publication in the journal although some revisions are needed. The main strengths of this paper are that it addresses an interesting and very timely question and provides a clear answer, with some limitations.

We suggest a linguistic revision and the addition of some references for a matter of consistency. Moreover, the authors should better clarify some points.

Author Response

The treatment landscape for several tumor types has changed dramatically over the last decade; for example, as regards renal cell carcinoma, the standard of care has shifted from monotherapy, typically a multi-targeted tyrosine kinase inhibitor (TKI), to combination therapies including immune checkpoint inhibitors (ICI).

Thus, the study addresses a timely topic.

Some changes are necessary in my opinion:

• Introduction section: although the authors correctly included important papers in this setting, we believe the background of sunitinib in medical oncology should be better explained and some papers should be cited within the introduction ( PMID: 34265504), only for a matter of consistency. We think it might be useful to introduce the topic of this interesting study.
  • Thank you for this suggestion. A paragraph tackling suggested topic of the background and the current role of sunitinib was made as follows:

    "A recent meta-analysis on therapeutic alternatives to first-line sunitinib monotherapy in mRCC patients demonstrated benefit of using combined immune-therapy with checkpoint inhibitors [6]. Careful approach should be taken in patients with dysregulated immune activation such as pre-existing autoimmune diseases or hematopoietic/solid organ transplant or compromised immune function (long-term immunosuppression, chronic viral infections), and/or significant medical co-morbidities (organ dysfunction, elderly or frail patients, metastatic brain disease) [7]. However, these patients and possibly those with favourable risk may still benefit from sunitinib monotherapy [8]. Furthermore, benefit of selective sequential treatment strategy has been suggested [7]."

Methods and Statistical Analysis: nothing to add.

• Discussion section: Very interesting and timely discussion. Of note, the authors should expand the Discussion section, including a more personal perspective to reflect on. For example, they could answer the following questions – in order to facilitate the understanding of this complex topic to readers: what potential does this study hold? What are the knowledge gaps and how do researchers tackle them? How do you see this area unfolding in the next 5 years? We think it would be extremely interesting for the readers.
  • The issues concerning the Discussion were comprehensively addressed as follows:

"However, more prospective studies need to be conducted to clarify underlying pathophysiology of this phenomenon that would include regular vitamin B12, folic acid and iron metabolism parameters together with evaluation of blood smear microscopy for possible abnormalities in blood cell morphology. Concurrent analysis of both TK inhibitors that target c-kit (e.g. axitinib, pazopanib also used in the treatment of RCC) and those that do not may provide clinically relevant data."

• • The following part of the discussion was reworded as follows (specifically addressing the suggestions):

"Novel approaches emerge in the treatment of RCC including immune-therapy or sequential therapies that phase out TK-inhibitor monotherapy in RCC patients. It follows that new surrogate biomarkers may be of help in identifying agent-specific toxicities in combination, i.e., sunitinib-containing therapies.

Studies on the pediatric population treated with sunitinib yielded limited results mostly due to the complexity of the treatment context, a limited number of patients, and ethical concerns as well [9-11]. Despite that, we were able to collect limited but relevant data demonstrating that the pharmacological mechanism behind this epiphenomenon may not differ between adult and pediatric populations. Of note, sunitinib-induced elevation of MCV was apparently not affected by concomitant anti-cancer polychemotherapy in pediatric patients."

However, we think the authors should be acknowledged for their work. In fact, they correctly addressed an important topic, the methods sound good and their discussion is well balanced.

• One additional little flaw: the authors could better explain the limitations of their work, in the last part of the Discussion.

  • We added “study limitations” paragraph in the discussion as follows:

"Our study has the following limitations. This was a retrospective study on a limited number of patients. We did not specifically address the pathophysiology of B12/folate-dependent red blood cell morphology as we did not have retrospective specimens available. The pediatric part of the study had even fewer patients included and, therefore, fewer observations available. Due to the retrospective nature of this study, the respective specimen sampling was not fully standardized with respect to sampling times, adverse events, or clinical toxicity evaluations."

We believe this article is suitable for publication in the journal although some revisions are needed. The main strengths of this paper are that it addresses an interesting and very timely question and provides a clear answer, with some limitations.

• We suggest a linguistic revision and the addition of some references for a matter of consistency. Moreover, the authors should better clarify some points.
  • The language was reviewed by an expert in scientific English writing. Thanks for all your comments.

Reviewer 2 Report

Sunitinib and several other tyrosine-kinase inhibitors influence erythrocyte mean corpuscular volume parameter (MCV) . Initial considerations about this phenomenon included possible relative folate and cobalamin deficiency. However, more recent studies provided data that this effect is related to the inhibitory activity of tyrosine-kinase inhibitors towards c-KIT, which is extensively expressed by progenitor cells in the bone marrow. This theory is supported by results of studies where imatinib, sunitinib, and pazopanib (c-KIT inhibitors) treatment is associated with a statistically significant rise in MCV, whereas sorafenib, erlotinib, and vemurafenib (no c-KIT inhibitory activity) showing no such association.

Based on above, the authors reported this study on “Sunitinib-induced elevation of mean corpuscular volume (MCV) – exploring dynamics of a potential marker of treatment adherence, therapy toxicity in adults and pilot data in pediatric cancer patients”

Personally, I reckon the manuscript is well written, however, it lacks cohesiveness and consistency. Some objectives were not examined and achieved.

My comments

1.      The title needs some rework. It reads like a full objective

Abstract

Sunitinib is a broad-spectrum tyrosine kinase inhibitor that is mainly used as second-line therapy for non-resectable gastrointestinal stromal tumors (GIST) and as a first-line treatment of metastatic renal cell carcinoma (mRCC) and as an "off-label" option in pediatric oncology. It has been previously reported that sunitinib significantly rises the mean corpuscular volume of erythrocytes (MCV) in treated subjects. The aim of this study was to assess time dynamics of this effect and evaluate possible links to clinical toxicity and, tentatively, therapeutic effect as well. In the study, 179 adult and 21 pediatric patients with solid tumors treated with sunitinib were retrospectively analyzed. The laboratory and treatment-related data were collected for each treatment period. The regression model with a broken-line relationship was used to fit time dependence of the MCV. In the adult group, MCV was increasing during the first 21.6 weeks (median) of treatment in a median level of 99.8 fl, where it stabilized. MCV increase was faster in the patients who suffered from treatment-related adverse events (21.3 vs. 24.6 weeks, p=0.010). In the pediatric cohort, the MCV dynamic was similar to adults. In conclusion, MCV dynamics during sunitinib treatment in pediatric and adult patients may provide clinical utility in monitoring treatment adherence and therapeutic drug monitoring.

Comment: The aim of this study was to assess time dynamics of this effect and evaluate possible links to clinical toxicity and, tentatively, therapeutic effect as well. -the aims should be phrased clearly, what are the reasons including both adult and ped patients?

MCV dynamics during sunitinib treatment in pediatric and adult patients may provide clinical utility in monitoring treatment adherence and therapeutic drug monitoring.=this trajectory of the findings seems too far-fetched

Table 5. Patient (left) and treatment period (right) characteristics and observed parameters of MCV time-courses of pediatric cohort.

Patients Characteristic N=21

Characteristic N=24

Comment: why there is N=24?

The standard treatment cycle of sunitinib was 50 mg/day in a 6-week course: 4 weeks on, 2 weeks off. Some patients had a dose reduction to 37,5 mg a day or 25 mg a day, respectively, due to possible drug-related adverse events. Dosage interruptions and adjustments for toxicity or intolerance were performed according to the manufacturer's recommendations

Furthermore, a cohort of pediatric patients treated with sunitinib in an individual "off-label" regimen at the Department of Pediatric Oncology of University hospital Brno for various types of malignancy between years 2012-2019 was selected with the same inclusion and exclusion criteria as described for adults. However, pediatric patients did not have standardized treatment protocols and the dosing was mostly adjusted according to the age, body mass, treatment tolerance and clinical toxicity. In this group, the main goal was to describe the dynamics of MCV since the authors were not aware of any previous publication describing this phenomenon in pediatric patients to date.

Comment: pls include the dosage used by the Ped group; also what is the reason of including the pilot ped group here in this study? 

Author Response

Sunitinib and several other tyrosine-kinase inhibitors influence erythrocyte mean corpuscular volume parameter (MCV) . Initial considerations about this phenomenon included possible relative folate and cobalamin deficiency. However, more recent studies provided data that this effect is related to the inhibitory activity of tyrosine-kinase inhibitors towards c-KIT, which is extensively expressed by progenitor cells in the bone marrow. This theory is supported by results of studies where imatinib, sunitinib, and pazopanib (c-KIT inhibitors) treatment is associated with a statistically significant rise in MCV, whereas sorafenib, erlotinib, and vemurafenib (no c-KIT inhibitory activity) showing no such association.

Based on above, the authors reported this study on “Sunitinib-induced elevation of mean corpuscular volume (MCV) – exploring dynamics of a potential marker of treatment adherence, therapy toxicity in adults and pilot data in pediatric cancer patients”

Personally, I reckon the manuscript is well written, however, it lacks cohesiveness and consistency. Some objectives were not examined and achieved.

My comments

• The title needs some rework. It reads like a full objective

  • Thank you for your review and this comment. The title was rephrased as follows:

    Sunitinib-induced elevation on mean corpuscular volume (MCV) - exploring its clinical relevance in cancer patients
• Abstract

Comment: The aim of this study was to assess time dynamics of this effect and evaluate possible links to clinical toxicity and, tentatively, therapeutic effect as well. -the aims should be phrased clearly, what are the reasons including both adult and ped patients?

MCV dynamics during sunitinib treatment in pediatric and adult patients may provide clinical utility in monitoring treatment adherence and therapeutic drug monitoring.=this trajectory of the findings seems too far-fetched

• • The abstract has been modified to be more clear with better-described aims.

  • The issue on the pediatric part of our manuscript was remade as follows (in the discussion section):Studies on the pediatric population treated with sunitinib yielded limited results mostly due to the complexity of the treatment context, a limited number of patients, and ethical concerns as well [9-11]. Despite that, we were able to collect limited but relevant data demonstrating that the pharmacological mechanism behind this epiphenomenon may not differ between adult and pediatric populations. Of note, sunitinib-induced elevation of MCV was apparently not affected by concomitant anti-cancer polychemotherapy in pediatric patients.

• Table 5. Patient (left) and treatment period (right) characteristics and observed parameters of MCV time-courses of pediatric cohort.

Comment: why there is N=24?

• • The right side of the table concerns treatment periods. There is N=24 because 3 patients had two treatment periods.

• Comment: pls include the dosage used by the Ped group; also what is the reason of including the pilot ped group here in this study? 

  • At the Department of Pediatric Oncology this drug is occcasionally used in an off-label use in patients with no higher priority treatment available. Therefore we were able to collect some pediatric data on this topic and we think that they may be of interest to readers from the field of pediatric oncology. In essence, we assume that the pharmacological mechanism behind this epiphenomenon may not differ between adult and pediatric populations. The context of sunitinib use in pediatric cancer patients was always more complex due to drug combination therapy in contrast with predominant monotherapy in adult population.

    In reply to dosing regiment request: A paragraph about dosing in pediatric group was added to Methods as follows:

    In the pediatric cohort, individual dosing regimens were employed and managed according to body surface area (BSA), age, and treatment tolerance, ranging from 7-32 mg/m²/day.

Reviewer 3 Report

1.       Patients with an insufficient number of blood collections for evaluation of selected parameter dynamics and those without sufficient data about the treatment were not included. Please clarify what is an insufficient number

2.       How did you fit the regression for change in MCV? As this is repeated measurement, did you used mixed effect model? Please provide more details.? How did you statistically identify the breakpoint value?

3.       "Our results confirmed a phenomenon of MCV elevation during treatment with sunitinib that appears to be vitamin B12 and folic acid independent favoring its suggested mediation through c-kit signaling pathway. "As your study did not investigate the mechanism of MCV elevation, and did not assess vitamin B12 and folic acid, I would be careful for this statement in conclusion

Author Response

1. Patients with an insufficient number of blood collections for evaluation of selected parameter dynamics and those without sufficient data about the treatment were not included. Please clarify what is an insufficient number

   • We fully understand this comment. Unfortunately, we can not precisely define the number. It is based on an exploratory analysis taking into account the number of measurements and their time distribution.

2. How did you fit the regression for change in MCV? As this is repeated measurement, did you used mixed effect model? Please provide more details.? How did you statistically identify the breakpoint value?

   • Thank you for this comment. Individual treatment periods were fit using linear regression models with segmented relationships between the response and explanatory variable, including breakpoint value identification. The reference describing this method is now included in the Methods section. The common relationship was fitted with a mixed effect linear model. This fact is now described in the Methods section. Some results have been slightly updated in accordance with the methodology.

3.      "Our results confirmed a phenomenon of MCV elevation during treatment with sunitinib that appears to be vitamin B12 and folic acid independent favoring its suggested mediation through c-kit signaling pathway. "As your study did not investigate the mechanism of MCV elevation, and did not assess vitamin B12 and folic acid, I would be careful for this statement in conclusion

   • We agree with the comment. As is, it sounds like a presumptive statement not based on mechanistic studies. The issue was addressed in the discussion and we added a study limitations paragraph commenting on it. The wording of the Conclusions was rephrased as follows:

"We describe a phenomenon of MCV elevations occurring in the course of treatment with a multitargeted tyrosine kinase inhibitor sunitinib. This is an apparent drug-related epiphenomenon where the underlying pharmacological mechanism may go through c-kit signaling pathway inhibition. We present a regression model of this phenomenon for standard dosing that may serve as an additional but perhaps valuable surrogate marker for therapeutic drug monitoring and treatment adherence indicator for pediatric and adult patients. Adult patients that develop any adverse events appear to have a faster MCV increase rate than those reporting no adverse event hence suggesting its possible clinical utility as an indicator of therapeutic toxicity."

Round 2

Reviewer 1 Report

Acceptance.