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Prophylaxis with trimethoprim-sulfamethoxazole (TMP-SMX) decreases the incidence of interstitial pneumonia (IP) in B cell non-Hodgkin lymphoma (NHL) patients receiving chemotherapy with rituximab

Background Several studies have reported on the incidence of interstitial pneumonia (IP) among patients with non-Hodgkin lymphoma (NHL) that have been treated with chemotherapy plus rituximab, however, the best means of prophylactically preventing IP remains unclear. This retrospective study was designed to explore the prophylactic effect of trimethoprim-sulfamethoxazole (TMP-SMX) on IP and to identify IP-associated risk factors in NHL patients. Methods Between March 2013 and April 2018, 498 patients (264 male, 53%) with B cell NHL undergoing first-line rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (RCHOP)-like chemotherapy treatment were enrolled in this study. Results These patients had a median age of 56 years, and 311 of these patients (62.4%) were administered prophylactic TMP-SMX. IP occurred in 65 patients (13.1%), with once daily prophylactic TMP-SMX treatment leading to a significant reduced IP rate (21.4% vs. 8.0%; p<0.001). Among patients treated with TMP-SMX, 2 (1.2%) exhibited rashes, 38 (12.2%) suffered from nausea and vomiting, 52 (16.7%) showed signs of neutropenia, and 18 (5.8%) suffered kidney dysfunction. Being male, having a history of diabetes, and not having undergone prophylactic TMP-SMX treatment were all found to be significantly associated with IP risk in both univariate and multivariate analysis. Disease progression was observed in 55/311 (17.7%) patients that underwent prophylactic TMP-SMX treatment and in 63/187 (33.7%) patients that did not (p<0.001). Conclusions Overall, these results reveal that IP is common in B cell NHL patients undergoing chemotherapy plus rituximab treatment, with the prophylactic administration of once daily oral TMP-SMX significantly reduces the IP incidence.


Background
The combination of CHOP chemotherapy plus rituximab has been widely employed for treatment of CD20+ non-Hodgkin lymphoma (NHL) [1][2][3] . Previous studies have reported that 1.3 -14% of patients treated with chemotherapy regimens including rituximab develop interstitial pneumonia (IP) [4][5][6][7] . IP is a heterogeneous group of disorders that are classified together owing to their similar clinical, radiographic, physiologic, or pathologic manifestations 8 . IP can be caused by many reasons and can ultimately lead to dyspnea, respiratory failure, and even death. Individuals diagnosed with IP are more likely to stop undergoing further chemotherapeutic treatment, thereby reducing the efficiency of chemotherapy and shortening patient survival 9 . Therefore, active treatment and effective prevention of IP is essential in patients undergoing immunochemotherapeutic treatment.
Combination treatment with chemotherapy plus rituximab has the potential to inhibit patient immune functionality, thereby increasing the risk of opportunistic infection.
Several studies have concluded that the occurrence of IP is at least partially associated with a rising risk of pneumocystis carinii pneumonia (PCP) infection [4][5][6]10,11 . However, the most effective prophylactic drugs and methods for preventing IP remain controversial.
Trimethoprim-sulfamethoxazole (TMP-SMX), an oral broad-spectrum antibiotic, is a specific therapeutic and prophylactic agent that is used for the treatment of PCP infections 5,6,11 .
At our hospital, we have routinely administered prophylactic TMP-SMX to hundreds of lymphoma patients since 2013. In this study, we present a retrospective analysis of the impact of TMP-SMX prophylaxis on IP incidence among B cell NHL patients undergoing treatment with a combination of chemotherapy plus rituximab.

Participants and data collection
Study inclusion criteria were as follows: patients were diagnosed with CD20+ B cell non-Hodgkin lymphoma by a local pathologist according to WHO criteria 12 . All patients had undergone treatment with rituximab plus CHOP-like chemotherapy for at least two cycles.
Patients with T cell lymphomas were excluded from this study. Chemotherapy regimens other than RCHOP-like regimens were also excluded. Patients for whom full treatment data were not available were excluded from this analysis. As a control group, we included patients that had not undergone prophylactic TMP-SMX treatment. All of these randomly selected control patients had been diagnosed with untreated B-cell NHL and had been treated with first-line RCHOP-like chemotherapy for at least two cycles. For patients undergoing prophylactic TMP-SMX treatment, TMP-SMX was taken once daily from the time of treatment initiation until completion of chemotherapy. Each tablet contained 0.08 g TMP and 0.4 g SMX. TMP-SMX was not administered to patients with allergies to the drug, megaloblastic anemia, or severe liver or kidney damage. Prophylactic granulocyte colonystimulating factor (G-CSF) and antiemetic administration was allowed. Radiographic documents and data regarding patient clinical characteristics, histological diagnoses, chemotherapy regimens, and survival outcomes were retrospectively collected from the original computerized medical files. This trial was approved by the research ethics boards of Zhejiang cancer hospital, with all patients having giving written informed consent.

IP Diagnosis and treatment
The observation period for IP in this study extended from the first day of immunochemotherapy to 8 months after completion of immunochemotherapy. Routine imaging evaluations were performed every two cycles during chemotherapy and every 3 months after chemotherapy within the observation period. Patients underwent thoracic computed tomography (CT) scans when they exhibited symptoms of pulmonary infection.
IP was diagnosed via a multidisciplinary approach based upon clinical symptoms, laboratory tests, radiologic imaging, and pathologic findings. IP typically presented in the form of diffuse pulmonary interstitial infiltrates with reticular or ground-glass opacity, alveolitis, and the presence of diffuse infiltrates on CT scans. 11,13 When IP was suspected, laboratory tests measuring blood cell counts, C-reactive protein (CRP), procalcitonin (PCT), 3-b-D glucan antigens, Gram-negative lipopolysaccharides, Galactomannan antigen detection (GM), and bacterial culture were conducted to facilitate an appropriate diagnosis. Once they had been diagnosed with IP, patients began undergoing empirical treatment with a combination of antibiotics, antifungal agents, and glucocorticoids.
Ganciclovir was given when viral infection was suspected. When PCP was suspected, a therapeutic dose of TMP-SMX was administered. CT scans were conducted weekly until complete interstitial infiltrate absorbance was evident. After patients recovered from IP, retreatment with chemotherapy and/or rituximab was allowed. TMP-SMX was administered at prophylactic doses as described previously. Parameters relating to clinical presentation, diagnosis, causative pathogen, treatments, and outcomes were additionally summarized for all patients as appropriate.

Statistical analysis
For this study, overall survival (OS) and progression-free survival (PFS) were measured, with the former corresponding to the amount of time between starting chemotherapy and last follow-up or death due to any cause, and the latter corresponding to the period of time between the start of chemotherapy and the last follow-up, cancer progression, or allcause death. The National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTCAE) v 4.0 criteria were used for the gradation of all adverse events (AEs). χ2 tests were used to compare categorical variables between patient groups. A binary logistic regression was used to conduct univariate analyses with appropriate hazard ratios (HRs) and 95% confidence intervals (CIs). Each variable with a p<0.05 in the initial univariate analysis was incorporated into a multivariable model. p<0.05 was the significance threshold. SPSS 23.0 was used for all statistical testing.

Patient characteristics
Between March 2013 and April 2018, a total of 498 patients were analyzed for this study of whom the majority (264/498; 53%) were male. The clinical characteristics of these patients are compiled in Table 1 International Prognostic Index (IPI) did not differ significantly between groups.

Diagnosis and treatment of IP
IP occurred in 65 patients (13.1%), of whom 25 (38.5%) were in the TMP-SMX prophylaxis group. IP patients had a median age of 60 years (range: 18 -78), and exhibited the following pathological diagnoses: 57 cases of DLBCL, 1 of FL, 1 of MCL, 1 of CLL/SLL, 3 of MZL, and 2 of highly aggressive B cell lymphoma. IP incidence was significantly greater among patients that had not undergone prophylactic TMP-SMX treatment relative to those who did (21.4% vs 8.0%, p<0.001). The median time between the first day of immunochemotherapy and the date of IP diagnosis was 74 days, (range: 7 -158 days).
Prior to IP diagnosis, patients had been treated with a median of 3 cycles (range: 1 -8 cycles). The median cumulative dose of rituximab upon IP diagnosis was 2100 mg (range: 600 -4800 mg). A review of these 65 cases is shown in Table 2. Further chemotherapy and rituximab treatments were withheld immediately following IP diagnosis. The average time to IP remission was 12 days (range: 7 day to 58 days). No patients died as a consequence of their infection. After remission from IP, 21 patients completed further chemotherapy combined with rituximab, 35 patients received subsequent chemotherapy without rituximab, and 9 patients did not receive chemotherapy or rituximab. No patients suffered from the recurrence of IP following continued immunochemotherapy treatments.

Complications of prophylaxis
Of the 311 patients receiving prophylactic TMP-SMX, 2 (1.2%) had rashes, 38 (12.2%) suffered nausea and vomiting, 52 (16.7%) exhibited neutropenia, and 18 (5.8%) suffered kidney dysfunction. No patients discontinued TMP-SMX prophylaxis as a result of these adverse reactions. As these patients were undergoing concomitant chemotherapy, it is difficult to determine whether these adverse reactions were specifically associated with TMP-SMX prophylaxis in most cases.

IP Risk factors
We next sought to identify clinical parameters that were associated with IP risk in this patient population (Table 3). In a univariate analysis, we found that being male, having a history of diabetes, and not receiving TMP-SMX prophylactic therapy were all associated with elevated IP risk, and in a subsequent multivariate analysis all these three variables were found to independently predict a higher risk of IP.

Discussion
As the combination of chemotherapy plus rituximab has been employed with increasing frequency for the treatment of NHL, reports of treatment-associated IP have similarly become increasingly common. However, the exact incidence of IP among lymphoma patients remains uncertain owing to high variability among previous studies. In one retrospective analysis of 2212 consecutive Chinese lymphoma patients, overall IP incidence was determined to be 3.75%, with rates of 3.9% (7/287) and 2.4% (76/925) in patients with Hodgkin and non-Hodgkin lymphoma, respectively 9 . However, in other studies the reported incidence of IP among NHL patients undergoing CHOP-based chemotherapy with or without rituximab has ranged from 1.3% in a study by Giselle  17 . These studies have also suggested that the addition of rituximab to therapeutic regimens may increase IP incidence. In the present study, we observed an IP incidence of 21.4% in patients not receiving any preventive treatment, with this rate being higher than that in previous reports. There are several possible reasons for this difference. As an anti-CD20 antibody with an extended in vivo half-life, rituximab possesses broad immunomodulatory activity. It can induce B cell apoptosis, alter complement activation, and induce cytokine release, thereby potentially interfering with normal cytotoxic T cell responses and immune functionality so as to elevate the risk of opportunistic infection 18 . In this study, all patients received rituximab and chemotherapeutic treatments simultaneously, which may have also contributed to our overall findings. As patients in this study were being actively monitored for IP, this too may have increased the overall IP incidence rate given that it led to disease detection in otherwise asymptomatic patients. Other possible causes for elevated IP rates include differences in the baseline characteristics of patient populations, the chemotherapy regimens administered, chemotherapeutic dose intensity, diagnostic techniques, the small size of previous studies, or the fact that we employed a longer observation period.
Therefore, our results suggest that there is clear value in administering prophylactic IP treatment to NHL patients undergoing RCHOP therapy. 21% PCP incidence and treated patients suffering a 0% incidence rate when TMP-SMX was administered either daily or 3 days per week 26,27 . More recently, many studies have confirmed the efficiency of TMP-SMX prophylaxis as a means of decreasing the incidence of PCP in adult patients with lymphoma and in pediatric oncology patients 15,[28][29][30][31] . A metaanalysis of twelve randomized trials found that TMP-SMX administration was linked to a 91% drop in the incidence of PCP, with a significant reduction in PCP-related mortality 23 .
Consistent with these findings, in the present study we found that prophylactic TMP-SMX treatment significantly decreased the incidence of IP in B cell lymphoma patients undergoing R-CHOP-like chemotherapy from 21.4% to 8.0% (p<0.001).
The optimal administration schedule for prophylactic TMP-SMX is not well defined. Most previous studies have concluded that intermittent dosing with TMP-SMX is an effective alternative prophylactic regimen. TMP-SMX is thus variously administered twice daily two times per week 30 , two consecutive days per week 28,32,33 , twice weekly 31 , or three days per week 27 . Intermittent TMP/SMZ is an effective means of preventing PCP and can lower associated costs and rate of fungal infections. However, this dosing is not universal, as in one study by Toshiro et al. patients were instead administered one TMP-SMX tablet daily throughout the course chemotherapy 15 . A meta-analysis concluded that lower doses of TMP-SMX were an effective means of improving tolerance without compromising primary prophylactic efficacy 34 . No differences between once-daily and thrice-weekly administration schedules have been found 23 . Patients in the present study were administered one tablet of TMP-SMX per day, and this approach was convenient and easy to implement.
According to previous reports, roughly 30% -40% of patients stop TMP-SMX therapy as a result of poor drug tolerance when receiving intermittent prophylactic treatment 35 . The most common adverse events linked with such discontinuation include skin rash, myelosuppression, nausea, fever, renal and liver toxicity, and hyperkalemia [36][37][38][39] . The observed adverse events associated with TMP-SMX prophylaxis in the present study were consistent with these previous reports, however the overall tolerance for this daily TMP-SMX regimen was high, with no instances of discontinuation due to adverse reactions.
Moreover, the incidence of leukopenia and nausea and vomiting was low, which may be explained by the fact that patients were allowed to receive prophylactic G-CSF injections after chemotherapy and antiemetic treatments in this study.
We found that a history of diabetes, being male, and not undergoing prophylactic TMP-SMX treatment were independent risk factors associated with IP incidence. In diabetic patients, hyperglycemia can affect the chemotaxis, adhesion, phagocytosis and intracellular bactericidal efficacy of immune cells. In addition, the thickening of the alveolar epithelium, vascular hyaline degeneration, and pulmonary microangiopathy that occurs in diabetic patients can affect lung function. These factors will damage immune function and thereby increase rates of opportunistic infections among patients with diabetes, who experience 30% more pneumonia-related mortality than do non-diabetic patient populations 40 . Males usually receive higher doses of rituximab, have a longer smoking history, and are more likely to have poorer basic lung function than females.
This study has several limitations, and as such caution is warranted when interpreting our results. For one, BAL, as an important auxiliary examination procedure, was not widely used in this study. Only 7 patients received BAL and PCP infections were not detected in any of these patients. As such, we lack sufficient evidence regarding the specific cause of IP in this patient population. Secondly, 8% of patients in this study developed IP even after prophylactic TMP/SMX treatment, suggesting that there can be other causes for this condition. As such, further prospective studies are needed in order to explore other prophylactic drugs and their optimal administration in NHL patients. In addition, the retrospective nature of this study increases the risk of unintentional bias, potentially explaining the observed discrepancies regarding the rates of side effects associated with TMP-SMX.

Conclusions
These results clearly demonstrate that IP occurs relatively frequently among B-cell NHL patients undergoing chemotherapy plus rituximab treatment. Based on the findings of this retrospective analysis, we conclude that once daily prophylactic TMP-SMX administration beginning at the time of immunochemotherapy initiation significantly reduces IP incidence in these patients.

Ethics approval and consent to participate
The study protocol was approved by the Ethic Committee of Zhejiang Cancer hospital, Hangzhou, China. The subjects have given their informed consent.

Consent for publication
All authors read and approved the final manuscript.

Availability of data and material
All data generated during this study are included in this published article. The datasets used during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.