Episode 10B: Impact of Trilaciclib on Chemotherapy Induced Myelosuppression (CIM) in ES-SCLC

In this Precision Medicine Perspectives series Addressing Myelotoxicity as a Consequence of Treatment for Extensive-Stage Small Cell Lung Cancer, experts discuss the impact of chemotherapy induced myelosuppression in patients being treated for extensive-stage small cell lung cancer and review current treatment options. Chemotherapy induced myelosuppression (CIM) can be a significant consequence for patients receiving chemotherapy for the treatment of extensive stage-small cell lung cancer (ES-SCLC). Mark A Socinski, MD, a medical oncologist specializing in thoracic malignancies, defines chemotherapy induced myelosuppression (CIM) and discusses the challenges faced when treating CIM. Dr Socinski explains the rationale for using trilaciclib in patients who develop CIM for ES-SCLC and also provides insight into how the data from the post-hoc analyses of trilaciclib for CIM in patients with ES-SCLC will impact clinical practice.

Targeted Oncology™: What are the currently available treatment options for patients with extensive stage small cell lung cancer (ES-SCLC)?

Dr Socinski: The currently available treatment options for patients with extensive-stage small cell lung cancer really were framed by two trials, the IMpower133 trial and the CASPIAN trial. What these trials did is take the doublet of platinum plus etoposide, which has been a standard of care for decades, [and] essentially in the case of IMpower133 added atezolizumab onto that platform. In the case of CASPIAN, [it was] durvalumab. Both of these trials were positive for overall survival [and the overall survival was] consistent between these two randomized trials. [These trials] really transformed the standard of care from platinum-etoposide to the addition of either atezolizumab or durvalumab with very similar outcomes and benefits. With hazard ratios for overall survival in the 0.7 to 0.75 range, [there was] a significant improvement in overall survival.

Targeted Oncology™: Briefly define chemotherapy induced myelosuppression (CIM), and how does it manifest?

Dr Socinski: Regarding chemotherapy induced myelosuppression, we know that the regimen of platinum-etoposide does result in myelosuppression that can be quite significant. When we say myelosuppression, we are really talking about the three lineages of blood cells, namely neutrophils, platelets [and] red blood cells. Chemotherapy-induced myelosuppression can be detected on blood tests that we would conduct on a routine basis [or at] other times when patients present with fever and neutropenia, or when they develop extreme fatigue and are found to be anemic, or they have bleeding complications due to platelets. The spectrum of the way in which chemotherapy induced myelosuppression can occur can be quite wide.

Targeted Oncology™: What are some risk factors that may predispose patients to developing CIM?

Dr Socinski: One of the risk factors is aging [since] elderly patients have less bone marrow reserve. [Another risk factor is if the patient has had] prior treatments, particularly radiation treatment that may have been delivered to bones that have a lot of the bone marrow where these three [cell] lines are made, [or] other concurrent treatments or history of treatment in the past. [Also,] certain comorbidities that may have affected the bone marrow in the past could predispose patients to it [chemotherapy-induced myelosuppression]. The consequences can be quite significant and can be quite varied. It's important to be aware of the complications of chemotherapy induced myelosuppression and to anticipate them by [monitoring] blood counts during the course of treatment.

Targeted Oncology™: How do you typically treat CIM in patients with extensive stage small cell lung cancer (ES-SCLC)?

Dr Socinski: In the past, we have typically treated chemotherapy induced myelosuppression in the setting of extensive-stage small cell lung cancer in a reactive fashion. We would allow patients to become neutropenic or become anemic or thrombocytopenic, and then we would react to that either with transfusions or the use of growth factors, whether they would be white cell growth factors or red blood cell growth factors. Typically in the past it would be kind of a reactive strategy to these sorts of things.

Targeted Oncology™: What are some challenges seen when treating CIM in patients with ES-SCLC?

Dr Socinski: The consequences and some of the challenges in treating [CIM] is that patients often have consequences of the chemotherapy induced myelosuppression before you treat it. Therefore, we were allowing our patients to have a sequela of chemotherapy induced myelosuppression and then reacting to it. It would be much better to take a more proactive [approach and] that's really the rationale for using trilaciclib in patients who are receiving chemotherapy for extensive stage small cell lung cancer. Trilaciclib is a CDK 4/6 inhibitor. In this case, it's given intravenously over a short infusion. [Trilaciclib works by] arresting the bone marrow progenitor cells in the resting phase of the cell cycle G0, [so] these cells are not dividing and therefore they are protected against the cytotoxic effect of the chemotherapy when it is delivered. Because of the intravenous infusion and the short duration, the effect is very transient. Trilaciclib is administered only on the day of chemotherapy. [Trilaciclib] arrests the stem cells in the dormant phase to help protect the cells against the effect of chemotherapy.

Targeted Oncology™: Please review the post-hoc analysis of the impact of trilaciclib on CIM from the randomized trials in patients with extensive stage small cell lung cancer. Which trials were evaluated? Which CIM events were assessed and how were they defined?

Dr Socinski: As I mentioned, trilaciclib is a CDK 4/6 inhibitor [that] is given IV and is short-acting. [Trilaciclib] earned its FDA approval and indication in the setting of reducing the occurrence of chemotherapy induced myelosuppression across the three [cell] lineages, neutrophils, red blood cells, and platelets. This data was demonstrated in three phase 2 clinical trials that were placebo controlled [and] all of them in extensive-stage small cell lung cancer. Two [of the clinical trials were in] the first-line setting, [while the third clinical trial] was in the second-line setting, although there were a few patients that had received two prior regimens. We recently saw a post-hoc trial analysis that was really done to further assess the impact of trilaciclib on the occurrence of both, single as well as concurrent multi lineage chemotherapy induced myelosuppression events. [The analyses looked] at [the events] separately in terms of line of therapy, dividing it into first-line as well as second-line trials. In two of the first-line trials, [trilaciclib] was given with etoposide, carboplatin and atezolizumab in the first trial [and] just etoposide-platinum by itself in the second trial. Again, [the trials] were placebo controlled. Then in the second-line [and] third-line trial, [trilaciclib was given] with topotecan [and this trial was also] placebo controlled. The aim of the study was to look at the proportion of patients with single and concurrent multi lineage chemotherapy induced myelosuppression events and to estimate that per cycle and what happened over the first four cycles of chemotherapy. What was assessed was really the severe grade three or higher events of neutropenia, anemia, and thrombocytopenia.

Targeted Oncology™: How was concurrent CIM defined in this post-hoc analysis?

Dr Socinski: Concurrent chemotherapy induced myelosuppression events were defined as having two or three lineage-specific events that overlapped by at least a day or more. The results were pretty consistent with what we had seen in prior trials. When you compare trilaciclib to the placebo arm, fewer patients that were receiving trilaciclib had single lineage events with regard to chemotherapy induced myelosuppression [and] fewer patients had concurrent events in either two or three lineages during cycles 1 to 4 of the first-line trials. [There was a] similar trend seen in a second-line trial, although this was a smaller number of patients. Severe chemotherapy-induced events occurred more frequently in earlier cycles [and] that was true of neutropenia. As we typically see, severe anemia and thrombocytopenia tended to occur a little bit later. The conclusion of this post-hoc analysis was that those patients with extensive-stage small cell lung cancer receiving trilaciclib had fewer single lineage as well as concurrent multi lineage chemotherapy events compared to the placebo arm. This was a nice reinforcement of the initial data set that we saw from these trials in the original FDA approval.

Targeted Oncology™: What are the clinical implications of these post-hoc analyses of trilaciclib from randomized clinical trials?

Dr Socinski: How do we integrate the information from the post-hoc analysis into day-to-day practice? Now, some of us, like myself, had adopted the use of trilaciclib based on the original data [that] we saw from the registrational trial. I like to take the proactive approach rather than the reactive approach. My experience with using trilaciclib concurrently with chemotherapy has been pretty positive. I am convinced that it abrogated the complications of neutropenia [and I am] impressed [to see a] reduction in the occurrence of anemia. I think anemia is one of the driving factors that really impacts patient's quality of life.

Targeted Oncology™: Might the results of these post-hoc analyses change your clinical practice?

Dr Socinski: The post-hoc analysis really did not necessarily change my practice or my feeling about trilaciclib, [but] it reinforced it. Using [trilaciclib] reduces the single or concurrent suppression of the three lines of blood cells. I do think that that allows patients to have a more tolerable chemotherapy course. I would like to think it is a better quality of life since there is less fatigue, [and] less complications of anemia, which is a major issue from my perspective. [Also,] less complications with neutropenia [and] a lower rate of severe neutropenia, which would reduce the likelihood that you are going to have an episode of neutropenic fever in this setting. Again, like many of these post-hoc analyses, it really reinforced the initial messaging that we got from the trials. It just builds confidence that trilaciclib is an agent that does have a supportive care effect in this particular setting by reducing the risk of complications of chemotherapy induced myelosuppression.