Together these three market segments represent a significant commercial opportunity for imetelstat with a total addressable market of $3.5 billion by 2033 in the U.S., and these key European markets. This slide highlights the key attributes of imetelstat in the Phase 3 IMerge trial that resonated most strongly with community and academic hematologists. Our unprecedented, IMerge Phase 3 data that highlights totality of clinical benefit, achievement of transfusion independence, regardless of RS subtypes, and meaningful durability of response, along with the PRO data that highlighted improvement in fatigue, when treated with imetelstat, resonate highly with physicians and serve as critical differentiators and form our value proposition. We continue to work towards bringing all of these elements along with the real-world analysis of the importance of achieving transfusion independence to our payers and prescribers through appropriate channels to highlight the imetelstat value proposition.
This next slide highlights key aspects of our market research with hematologists from both the U.S. and key European markets. First, imetelstat first-in-class mechanism of action is seen as the key driver for future market adoption. Together with the durability of response, physicians view the opportunity for a new and novel mechanism as highly compelling. Second, imetelstat is projected to be part of the standard of care across both RS negative and RS positive patients’ subgroups. Physicians express a clear preference to use imetelstat first for their frontline RS negative ESA ineligible patients and across all this luspatercept prior treated patients. Third, in the ESA relapsed refractory patients segment physicians note that imetelstat demonstrates significant improvements in long-term response.
That is the 24-week transfusion independence over available options especially in the RS negative patients. Fourth, for high transfusion burden patients relapsed and refractory low risk MDS patients, physicians believe imetelstat may be a compelling option over currently approved therapies. This next slide highlights the results from the survey we conducted post luspatercept frontline commands data release. This was done with 50 plus practicing hematologists in the U.S across both community and academic settings to understand how they would use imetelstat if available as compared to other available therapies. On the left-hand side of this slide, you can see that the responses indicate strong enthusiasm for imetelstat to be integrated across the three different patient segments in the low risk MDS treatment landscape upon potential approval.
The graph on the right-hand side shows responses further segmented for RS positive and RS negative patients within the subgroups. The responses, as you can see here, indicate that imetelstat is not only expected to be broadly adopted for the treatment of low risk MDS, but that it is especially likely to become a new standard of care for second line RS negative patients. As a reminder, the RS negative patient segment is approximately 3x larger than the RS positive patient segment and treatment options for RS negative patients remain sub-optimal. Holistically, we believe that the qualitative market research shown earlier and quantitative survey highlighted here are highly aligned with the updated NCCN guidelines. These results emphasize the significant unmet treatment needs across the low risk MDS patient population.
Therefore, we strongly believe that imetelstat if approved, can play a meaningful role in the treatment paradigm of low risk MDS moving forward. We believe that we are well positioned to execute against this tremendous potential commercial opportunity. I have described in detail in the past the robust internal planning to prepare imetelstat, the market and Geron as an organization so that we can deliver a seamless customer experience to all stakeholders, while ensuring broad reimbursement for imetelstat. With regards to U.S. launch planning, with our PDUFA date of June 16, 2024, in hand, we expect to be ready to launch upon potential FDA approval. Significant progress on multiple fronts is highlighted on this slide. We have been highly successful in attracting deeply experienced talent to Geron with significant operational and U.S. launch experiences.
Our non-field facing commercial organization is now fully deployed and deeply engaged in bringing imetelstat to the U.S. market. We plan to hire our field facing teams, including our sales force in quarter one, 2024 to ensure proper time for onboarding and training. We have already identified many talented and experienced individuals who are eager to join the team and are very much looking forward to welcoming this critical function to Geron next year. We are pleased with our progress to date and look forward to sharing updates in the future. I will now turn the call over to Michelle for a financial update. Michelle?
Michelle Roberston: Thanks, Anil, and good morning everyone. As this is my first earnings call at Geron, I wanted to start by saying how very excited I am to be part of this amazing team and how privileged I feel to lead the finance function through this pivotal time for the company. With regards to Q3 financial, for detail results, please refer to the press release we issued this morning, which is available on our website. I will now review some highlights from the quarter. At the end of Q3, our cash, cash equivalents and marketable securities were $381.9 million. This balance includes approximately $28.3 million in proceeds from warrant exercises in the third quarter. There are approximately 2.5 million warrants outstanding and the potential proceeds from these warrants is $3.2 million.
R&D expenses for the three and nine months ended September 30 were 29.4 million and 92.1 million respectively, compared to 24.6 million and 67.3 million for the same period in 2022. Expenses have increased year-over-year primarily related to supporting our clinical trials IMerge Phase 3, and IMpactMF. Both personnel and consulting costs increased and support regulatory submissions, and increased investment in manufacturing as we prepare for the potential commercialization and transfusion dependent lower risk MDS. G&A expenses were 18.4 million and 47.7 million for the three and nine months ended 9/30/2023 compared to 15.6 million and 29.8 million for the same period in 2022. The increase in G&A expense is primarily attributed to headcount and external expenses to support the commercial readiness activities.
At the end of September 30, the company had headcount of 137 employees, which we projected to grow to approximately 160 by the end of 2023. Our projected full year 2023 GAAP operating expenses are expected to be between $200 million and $210 million. Moving forward, we plan to provide only GAAP guidance for consistency with our SEC financial. Based on our current operating plans and expectations regarding the timing of potential approval of our imetelstat NDA that is currently under FDA review and subsequent potential U.S. commercial launch. We believe that our current cash runway together with projected revenues from U.S. sales of imetelstat proceeds from the exercise of outstanding warrants and funding under our loan facility will be sufficient to support our operations through the end of the third quarter of 2025.
