Background: Acute lymphoblastic leukemia (ALL) is a common malignant neoplasm in children. Although chemotherapy achieves remission in over 70% of cases, it can cause gastrointestinal toxicity in up to 32.5%. Some studies suggest that administering probiotics reduces this risk, but the evidence remains inconsistent.

Objective: To evaluate the effectiveness and safety of administering L. casei, L. rhamnosus or B. bifidum compared to a placebo for the prevention of gastrointestinal toxicity, decreased intestinal permeability, and changes in intestinal microbiota in pediatric patients diagnosed with acute lymphoblastic leukemia receiving chemotherapy.

Methods: A total of 120 participants aged 6 to 17 years, diagnosed with ALL and receiving consolidation phase chemotherapy without gastrointestinal comorbidities, will be included. Participants will be administered daily 2 capsules containing either 1) L. casei, 2) L. rhamnosus, 3) B. bifidum or 4) placebo daily for 8 weeks. The clinical status of the participants will be evaluated weekly by the oncology service to determine the presence of gastrointestinal toxicity and adverse events. Changes in intestinal permeability will be assessed by measuring beta-lactoglobulin in a blood sample using the ELISA technique, while changes in the intestinal microbiota will be analyzed by genomic sequencing at baseline and at the end of follow-up.

Statistical analysis: Descriptive analysis will use measures of central tendency and dispersion. For quantitative variables, the mean and standard deviation or median with minimum and maximum values will be calculated depending on the distribution type. Frequencies and proportions will be calculated for qualitative variables, presented in tabular and graphical form. To compare the quantitative variables between the four interventions, a multi-way ANOVA test will be used.

The risk of gastrointestinal toxicity and adverse events will be analyzed by calculating the relative risk and 95% confidence interval. Differences between the interventions will be analyzed using survival analysis with the Kaplan-Meier and Log-Rank tests. Sequencing data will be analyzed using the Qiime2 program, filtered to generate a phylogenetic tree using the Silva database. Corresponding plots will be generated for each taxonomic level. Alpha (intra-group) and Beta (inter-group) diversity will be presented by ordination plots using principal component analysis with the ANCOM program

Background Acute lymphoblastic leukemia (ALL) is a malignant disease characterized by the uncontrolled proliferation of immature lymphoid cells. It is the most common neoplasm in children, representing up to 53.1% of all oncologic processes in Mexico [1-6]. Fortunately, with the current chemotherapeutic treatments, disease remission is achieved in 98% of cases; however, the chemotherapeutic treatments have side effects that can lead to gastrointestinal toxicity (7.7 to 32.5%), which is associated with up to 50% mortality.

Among the most common gastrointestinal manifestations resulting from this toxicity are mucositis, pancreatitis (2 to 8%), diarrhea (10 to 82%), and colitis associated with decreased Bacillus spp and Bidifobacterium spp, increasing the risk of necrosis and intestinal perforation of the terminal ileum and cecum. Hence, several studies have been conducted to identify agents that can reduce the incidence of gastrointestinal toxicity like as probiotics which are a group of saprophytic microorganisms (bacteria, viruses, fungi and protozoa) that live in equilibrium on the skin and mucous membranes, mainly in the intestine, have garnered attention.

Probiotics are known to have several beneficial functions such as promoting the absorption of carbohydrates, short-chain fatty acids and calcium; facilitating the synthesis of lipids and vitamins; modulate and reduce the concentration of inflammatory mediators in the intestinal mucosa; improve mucosal blood flow, thus reducing the risk of ischemic areas in the intestine; and strengthen the immune system.

Although research has been conducted on the use of probiotics to prevent or reduce the toxic effects of chemotherapy, the results are still inconclusive because the effect of probiotics has been analyzed in multiple combinations, which makes it difficult to distinguish the specific effects per phylum. This complicates the generation of standardized therapeutic schemes to improve the quality of care of these patients. If this project successfully identifies the effectiveness and safety of these probiotics, it will enable to development of new therapeutic strategies aimed at improving the quality of healthcare for these patients, reducing the frequency and severity of gastrointestinal complications secondary to the administration of chemotherapy.

Objective To evaluate the effectiveness and safety of the administration of Lactobacillus casei, Lactobacillus rhamnosus and Bifidobacterium bifidum compared to placebo in reducing the risk of gastrointestinal toxicity, decreasing intestinal permeability, and changing intestinal microbiota without the development of adverse effects in pediatric patients diagnosed with ALL receiving consolidation chemotherapy in the Oncology Service of the Instituto Nacional de Pediatría.

General Description of the Study

1. Participant selection and consent:

   • Participants meeting the study selection criteria will be selected.
   • Informed consent will be obtained from the participant's parents or guardians and, if appropriate, from the patient if older than 8 years of age. They will be informed about the benefits, complications and adverse effects of the interventions (Appendix 1-3).
   • If the parents or guardians prefer treatment outside the research project, the patient will be treated according to the established national protocols used in the Oncology Service of the Instituto Nacional de Pediatría.
   • Consent will also be obtained for the use of personal data as per Appendices 4 and 5. This data includes participant and parent names, birth date, sex, CURP, address, contact number, medical history, general habits, pathological conditions, social conditions, to be used exclusively for this research project.
   • Data will be handled with strict confidentiality, stored in an electronic database for five years by project personnel.

2. Initial Assessments:

   • A pediatric oncologist will perform a medical history, physical examination, anthropometry, fecal and serum sampling.
   • A nutritionist will evaluate the participant´s nutritional status and body composition.

   A) Physical examination:

   • Participant will remove outer clothing and shoes and sit on the examination table.
   • The pediatric oncologist will visually inspect for skin lesions using a lamp and tongue depressor if necessary.
   • Body temperature will be measured with a digital thermometer.
   • Participants will lie supine for palpation, percussion, and/or auscultation to assess cardiac, and abdominal conditions.

   B) Anthropometry

   • Weight will be measured three times using a Seca scale.
   • Height will be measured three times using a stadiometer.
   • Waist circumference will be measured at the midpoint between the lower edge of the last rib and the upper edge of the iliac crest.
   • Hip circumference will be measured 15 cm below the waist.
   • Arm circumference will be measured around the biceps muscle.
   • Thigh circumference will be measured around the upper third of the thigh.

   C) Nutritional Status

   - Height-for-Age (H-A), Weight-for-Age (W-A), Weight-for-Height (W-H), and Body Mass Index (BMI) indices will be classified according to NOM-008-SSA2-1993 standards.

   D) Body composition

   • Participants will remove metallic objects, empty their bladder, and lie supine on a non-conductive bed.
   • Electrode placement will be prepared with a cleansing towel and an electrically conductive towel.
   • Electrodes will be placed on hands and feet, and a multifrequency bioelectric impedance device will measure body composition at six different frequencies.
   • Data will be adjusted to WHO percentile curves.

   E) Fecal samples

   • Participants will collect stool samples at home using provided kits and instructions.
   • Samples will be transported in a cooler to the Instituto Nacional de Pediatría on the same day for analysis and will be stored in the freezer at -70°C until the end of the project.

   F) Serum samples

   • A 3 ml blood sample will be collected by peripheral venipuncture.
   • Serum samples will be processed to determine antibodies against beta-lactoglobulin using the sandwich enzyme immunoassay technique.

   Assessments will be conducted weekly for clinical condition, anthropometry, and body composition at weeks 1, 4, and 8, and fecal and serum samples at weeks 1 and 8.

3. Preparation of interventions:

   • Interventions will be prepared in a Baker Company Class II Type A2 vertical laminar flow hood.
   • The required amounts of lyophilized probiotic powder and microcrystalline cellulose will be mixed for 5 minutes (2:30 clockwise and 2:30 counterclockwise) at a speed of 25 rpm and encapsulated at a dose of: L. casei and L. rhamnosus at 2.5 billion CFU per capsule, B. bifidum at 1 billion CFU per capsule and placebo 300 mg of microcrystalline cellulose.
   • Each intervention will be stored in labeled sterile bags and refrigerated at 2 to 8°C.
   • Capsules will be quality checked for UFC content at Bacteriology Laboratory by dilution and sequencing, and any deviations will result in process adjustments.

4. Participant Allocation:

   • Participants will be randomly assigned to interventions using a computer-generated sequence, adjust in balanced blocks of five. (Appendix 7).
   • An external researcher will place intervention names in opaque envelopes, labeled with random numbers of the sequence.
   • Participants will draw a random number to be assigned to an intervention, communicated to the principal investigator.

5. Intervention Administration:

   • Participants will receive bottles with 14-16 capsules of the assigned intervention, stored in a cooler with refrigerated gel packs.
   • Participants will take one capsule before breakfast and one before lunch for one week, recording adherence in a logbook and repeating this process for eight weeks.

6. Clinical Evaluation:

   - Weekly clinical evaluations will be conducted for mucositis, diarrhea, colitis, flatulence, abdominal distention, and constipation, graded according to the Common Terminology Criteria for Adverse Events (CTCAE) scale (V 4.02) [39]. If necessary, the pediatric oncologist will initiate treatment according to the Oncology service plan.

7. Data Collection:

   • If antibiotics are required or the chemotherapy consolidation phase is completed, participants will be eliminated from the study, and final assessments will be conducted.
   • Data from weekly clinical evaluations, nutritional assessments, and study follow-ups will be recorded in a data collection form (Appendix 8) and entered an electronic Excel database for statistical analysis using STATA 18 by a blinded researcher.

The sample size was calculated based on data from the study by Reyna-Figueroa, which reported a 0% incidence of diarrhea during the administration L. rhamnosus compared to 10% in participants who did not receive probiotics. Using the formula for proportions, with an alpha error of 0.05, 80% power, and estimating a loss rate of 20%, a sample size of 30 participants was determined for each of the four groups.

Statistical analysis A descriptive analysis will be performed using measures of central tendency to understand the characteristics of the studied sample and to determine the type of distribution of each variable using the Kolmogorov-Smirnoff normality test. For quantitative variables, the mean and standard deviation or median with minimum and maximum values will be calculated, depending on the type of distribution and summarized in tabular form; and data graphically represented by boxplot or bars chats as appropriate.

To compare the quantitative variables between the four interventions, a multi-way ANOVA test will be used. For qualitative variables, the chi-squared test will be used to compare the groups, adjusting for the nutritional status of the participants.

The risk of gastrointestinal toxicity and adverse events will be analyzed by the relative risk or Peto's odds ratio and 95% confidence interval. Differences between the interventions will be analyzed using survival analysis with the Kaplan-Meier and Log-Rank tests. Sequencing data will be analyzed using the Qiime2 program, filtered to generate a phylogenetic tree using the Silva database. Corresponding plots will be generated for each taxonomic level. Alpha (intra-group) and Beta (inter-group) diversity will be presented by ordination plots using principal component analysis with the ANCOM program.

Noted that patients who drop out of the study will have their results analyzed up to their last record, and all analyses will be conducted on an intention-to-treat basis.

Inclusion Criteria:

• Patients older than 6 years and younger than 17 years with a recent diagnosis of acute lymphoblastic leukemia, confirmed by bone marrow aspirate and interpreted by a pediatric oncologist.
• Participants of both sexes
• Participants receiving treatment at the Oncology Service of the Instituto Nacional de Pediatría.
• Receiving chemotherapy according to national health protocols in the consolidation phase.
• Informed consent
• Informed assent for those older than 8 years.

Exclusion Criteria:

• Allergy to probiotics.
• Consumption of another probiotic
• Enteropathies affecting intestinal absorption (e.g., malabsorption syndrome, short bowel syndrome, intestinal malrotation, chronic nonspecific ulcerative colitis, Crohn's disease).
• Chronic diarrhea (>15 days of duration)
• Presence of mucosal lesions
• Impossibility of enteral feeding
• Renal insufficiency
• Peritoneal dialysis
• Water and electrolyte disorders
• Surgical intestinal bypass (e.g., colostomy, ileostomy)
• Congenital metabolic disorders
• Septicemia
• Body temperature > 38° C
• Received broad-spectrum antibiotics (piperacillin/tazobactam, fourth generation cephalosporins, aminoglycosides, carbapenem and/or metronidazole) within the past 30 days.

Interventions packaged in identical, odorless, tasteless, opaque capsules; stored in identical white plastic bottles.