Exhibit 99.1

FOR IMMEDIATE RELEASE

INFINITY ANNOUNCES ADVANCEMENT OF LEAD DEVELOPMENT PROGRAM

AND THIRD QUARTER FINANCIAL RESULTS

— Highlights Include Evidence of Biological Activity of IPI-504 in a Phase 1 NSCLC study and

Establishment of Recommended Phase 2 Dose and Schedule of IPI-504 —

CAMBRIDGE, Mass. – October 29, 2007 – Infinity Pharmaceuticals, Inc. (NASDAQ: INFI), an innovative cancer drug discovery and development company, today announced results for the third quarter of 2007.

Recent accomplishments included:

“We’ve made great strides in all of our programs recently and are on track to achieve important milestones over the coming months,” said Steven H. Holtzman, chair and chief executive officer. “We have in place a scientific team with a demonstrated history of discovering and developing important new medicines for patients. We also have a business team with a track record of building companies and creating value.”

“We are delighted with the broad progress of our pipeline over the past quarter, especially with the evidence of biological activity of IPI-504 in a second disease setting,” added Julian Adams, Ph.D., president of research and development and chief scientific officer. “In the coming months, we expect to advance IPI-504 into the Phase 2 portion of the NSCLC trial, additional indications and combinations, and a potential registration trial.”

Research and Development Update

At the AACR-NCI-EORTC International Conference in October 2007, Infinity and MedImmune presented preliminary evidence of biological activity in a heavily pre-treated population of patients with advanced NSCLC, based on preliminary data from the open-label Phase 1/2 study of IPI-504. As reported, in seven of nine evaluable patients, disease stabilization by RECIST (Response Evaluation Criteria in Solid Tumors) was achieved over at least one cycle of administration. One patient with a mutation in epidermal growth factor receptor (EGFR) and prior history of progression on targeted kinase inhibitors experienced Stable Disease for more than 6 months. In addition, four of four evaluated patients who underwent positron emission tomography (PET) imaging revealed a decrease in tumor metabolic activity in response to IPI-504 administration as measured by uptake of 18-fluorodeoxyglucose, an imaging agent.

The Phase 2 portion of the NSCLC study, expected to begin before year-end, will evaluate a three-week cycle of administration at 400 mg/m ² consisting of twice-weekly treatment for two weeks followed by one week off treatment. In this portion of the trial, at least 20 patients (10 with and 10 without EGFR mutations) will be enrolled to further characterize safety and biological activity of IPI-504.

In the third quarter, Infinity and MedImmune completed the dose escalation portion of their open-label Phase I study of IPI-504 in patients with relapsed, refractory Gleevec ^® -resistant GIST and STS. The companies have initiated the expansion phase of the trial at the recommended Phase 2 dose and schedule of 400 mg/m ² on a twice-weekly dose administration for two weeks followed by one week off treatment. In this expansion phase, up to 20 additional patients (10 with GIST and 10 with STS) will be evaluated to further characterize safety and biological activity of IPI-504. At the American Society for Clinical Oncology Annual Meeting in June 2007, the companies presented data from the dose escalation portion showing that 16 of 21 evaluated patients (76 percent) had a best response of Stable Disease as measured by RECIST criteria.

Infinity and MedImmune have advanced their oral Hsp90 program and are in IND-enabling studies for both the oral formulation of IPI-504 and their second ansamycin class oral Hsp90 inhibitor, IPI-493. The companies expect to complete their analysis of comparative preclinical data over the coming weeks and anticipate filing an IND on the lead clinical candidate in early 2008.

On October 16, 2007, Infinity was issued a patent (U.S. Patent No. 7,282,493) by the United States Patent and Trademark Office broadly covering IPI-504 and other hydroquinone-containing ansamycin analogues useful for treating cancer. The patent includes composition of matter, pharmaceutical composition, method of treatment, and synthetic method claims.

Infinity and MedImmune have also been granted orphan drug designation for IPI-504 by both the U.S. Food and Drug Administration’s Office of Orphan Products Development and the European Medicines Agency Committee for Orphan Medicinal Products for the treatment of GIST.

Infinity and MedImmune have also advanced IND-enabling activities for IPI-926, the companies’ lead candidate in their Hedgehog pathway inhibitor program. The companies anticipate commencing clinical development of IPI-926 in 2008. In addition, Infinity has extended into November 2007 the period of time under which AstraZeneca PLC must either divest or obtain Infinity’s consent to continue AstraZeneca’s Hedgehog pathway research program.

Third Quarter Financial Results

On September 12, 2006, Infinity completed its reverse merger with Discovery Partners International, Inc. This transaction was treated for accounting purposes as a reverse asset acquisition and recapitalization. Therefore, the financial information described below reflects the historical results of the pre-merger Infinity and that of the combined company following the merger. This information does not include the historical financial results of Discovery Partners.

At September 30, 2007, Infinity had total cash, cash equivalents, and available-for-sale securities of $116.3 million.

Total revenue for the third quarter of 2007 was $7.5 million as compared to $6.0 million for the third quarter of 2006. The increase in revenue was primarily derived from the acceptance of compounds by Novartis under its technology access agreement with Infinity and the amortization for a full quarter of the up-front license fee received from MedImmune in conjunction with its strategic product development alliance with Infinity. Revenue for the third quarter of 2006 included license fees received upon the amendment of Infinity’s technology access agreement with Amgen in July 2006.

Research and development (R&D) expense was $8.2 million for the third quarter of 2007 as compared to $8.3 million for the third quarter of 2006. Any amounts reimbursable by MedImmune under the cost-sharing provisions of the collaboration agreement are offset against Infinity’s R&D expense. Therefore, Infinity’s R&D expense of $8.2 million for the third quarter of 2007 reflects overall R&D expenditures by Infinity of $11.7 million less $3.5 million in amounts reimbursable by MedImmune. Infinity’s R&D expense of $8.3 million for the third quarter of 2006 reflects overall R&D expenditures by Infinity of $9.3 million less $1 million in MedImmune reimbursable amounts. The decrease in R&D expense compared to the prior period is primarily due to the reimbursable amounts from MedImmune, partially offset by increases in development costs, clinical expenses and salaries and benefits, including stock-based compensation expense.

General and administrative expense was $2.9 million for the third quarter of 2007 as compared to $2.5 million in the third quarter of 2006. The increase in expenses reflects primarily higher stock-based compensation expense.

Infinity’s net loss for the third quarter of 2007 was $2.0 million as compared to a net loss of $4.7 million for the third quarter of 2006. The decrease in net loss was primarily driven by an increase in collaborative research and development revenue and an increase in interest and investment income.

Based on Infinity’s financial position at the end of the third quarter of 2007, and by virtue of its cost-sharing agreement with MedImmune on the Hsp90 and Hedgehog programs and the funding of the company’s Bcl-2 drug discovery program by Novartis, Infinity is able to spend aggressively on its R&D programs while managing its net cash burn rate. In the absence of any additional financings or business development activities, Infinity anticipates ending 2007 with at least $100 million in cash, cash equivalents, and available-for-sale securities, which is expected to be sufficient to support the company’s current projected operating plan through at least the end of 2009.

Conference Call on Tuesday, October 30, 2007 at 8:30 a.m. Eastern Time

Infinity management will host a conference call on Tuesday, October 30, 2007 at 8:30 a.m. EDT to provide a business update and discuss the quarter results. A live webcast of the conference call can be accessed in the Investor section of Infinity’s website at http://www.ipi.com. Callers may participate in the call by dialing 1-866-765-6327 (domestic) and 1-913-312-1500 (international) five minutes prior to the start time. An archived version of the webcast will be available on Infinity’s website for 30 days.

About Infinity Pharmaceuticals, Inc.

Infinity is an innovative cancer drug discovery and development company that is seeking to leverage its strength in small molecule drug technologies to discover, develop, and deliver to patients best-in-class medicines for the treatment of cancer and related conditions. For more information on Infinity, please refer to the company’s website at http://www.ipi.com.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. These statements involve risks and uncertainties that could cause actual results to be materially different from historical results or from any future results expressed or implied by such forward-looking statements. Such forward-looking statements include statements regarding future preclinical and clinical trial activity for IPI-504, IPI-493, and IPI-926; the timing of IND submissions for IPI-504, IPI-493, and IPI-926; estimates of 2007 financial performance and year-end cash balance; and the expectation that Infinity will have cash to support its current operating plan through at least December 31, 2009. Such statements are subject to numerous factors, risks and uncertainties that may cause actual events or results to differ materially from the company’s current expectations. For example, there can be no guarantee that any product candidate Infinity is developing will successfully complete necessary preclinical and clinical development phases, be approved for sale in any market or that, if approved, revenue from sales of such product will reach any specific level. In particular, management’s expectations could be affected by risks and uncertainties relating to: results of clinical trials and preclinical studies, including subsequent analysis of existing data and new data received from ongoing and future studies; the content and timing of decisions made by the U.S. Food and Drug Administration and other regulatory authorities and investigational review boards at clinical trial sites; Infinity’s ability to enroll patients in its clinical trials; Infinity’s dependence on its collaborations with MedImmune and Novartis; Infinity’s ability to obtain additional funding required to conduct its research, development and commercialization activities; unplanned cash requirements and expenditures; and Infinity’s ability to obtain, maintain and enforce patent and other intellectual property protection for any products it is developing. These and other risks which may impact management’s expectations are described in greater detail under the caption “Risk Factors” included in Infinity’s quarterly report on Form 10-Q for the quarter ended June 30, 2007, as filed with the Securities and Exchange Commission on August 9, 2007. Further, any forward-looking statements contained in this press release speak only as of the date hereof, and Infinity expressly disclaims any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise.

Gleevec ^® is a registered trademark of Novartis Pharmaceuticals. INFI-G

Infinity Contact: Monique Allaire

    617.453.1105

    Monique.Allaire@ipi.com

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EXHIBIT 99.2

FOR IMMEDIATE RELEASE

INFINITY AND MEDIMMUNE PRESENT PRELIMINARY PHASE 1 DATA DEMONSTRATING BIOLOGICAL ACTIVITY OF IPI-504, A NOVEL HSP90 INHIBITOR, IN ADVANCED NON-SMALL CELL LUNG CANCER

— Evidence of Disease Stabilization and PET Responses Reported from Phase 1 Clinical Trial; Phase 2 Enrollment Scheduled to Begin by Year-End —

— Preclinical Evidence of Activity of IPI-504 in Breast Cancer Models Also Presented —

CAMBRIDGE, Mass. and GAITHERSBURG, Md. – October 25, 2007 – Infinity Pharmaceuticals, Inc. (NASDAQ: INFI) and MedImmune, Inc. today announced preliminary results of an ongoing Phase 1/2 clinical trial of IPI-504, the companies’ lead heat shock protein 90 (Hsp90) inhibitor, in patients with advanced non-small cell lung cancer (NSCLC). Seven of nine evaluable patients receiving IPI-504 achieved disease stabilization over at least one cycle of administration, and four of four evaluated patients who underwent positron emission tomography (PET) imaging exhibited a decrease in tumor metabolic activity in response to IPI-504 administration. The data were presented yesterday at the American Association for Cancer Research-National Cancer Institute-European Organization for Research and Treatment of Cancer (EORTC) International Conference on Molecular Targets and Cancer Therapeutics in San Francisco.

“IPI-504 has been well-tolerated and has displayed promising signs of biological activity in this heavily-pretreated patient population,” said Lecia V. Sequist, M.D., M.P.H., division of hematology and oncology, Massachusetts General Hospital. “The Phase 2 portion of the trial will further explore this activity at a higher dose level in an effort to establish a new therapeutic option for patients who have this aggressive disease.”

At the conference, the companies also presented research in which IPI-504 demonstrated evidence of preclinical activity in both Herceptin ^® (trastuzamab)-sensitive and -refractory Her-2 positive breast cancer cell lines.

Phase 1/2 Clinical Trial in NSCLC

In the Phase 1 portion of the open-label trial conducted at the Massachusetts General Hospital Cancer Center and the Dana-Farber Cancer Institute, 12 patients received IPI-504 at three dose levels (150, 225, and 300 mg/m ² ) on a four-week cycle consisting of twice-weekly dose administration with no break in treatment; data were available for 11 patients. All 11 patients had Stage IV NSCLC with an average of 3.7 prior therapies. Evidence of biological activity in these patients was evaluated using both CT scans and PET imaging.

In seven of nine evaluable patients, disease stabilization by RECIST (Response Evaluation Criteria in Solid Tumors) was achieved over at least one cycle of administration. One patient with a mutation in the epidermal growth factor receptor (EGFR) and prior history of progression on targeted kinase inhibitors experienced extended stable disease over seven cycles (27 weeks); this clinical benefit satisfies one of the prospectively-defined endpoints for expansion into the Phase 2 portion of the trial (stable disease greater than 12 weeks). On this twice-weekly schedule of administration with no treatment break, IPI-504 was well-tolerated through the dose-escalation reaching a maximum tolerated dose of 225 mg/m ² .

In addition, four of four evaluated patients who underwent PET imaging revealed a decrease in tumor metabolic activity in response to IPI-504 administration as measured by uptake of 18-fluorodeoxyglucose, an imaging agent. Two of these patients had partial responses by PET according to criteria established by the EORTC, defined as a decrease in SUV _max of 25 percent or more compared to baseline (see below for a full explanation of PET imaging).

The Phase 2 portion of the trial is expected to begin by year-end with a goal of determining the potential anti-tumor activity of IPI-504 in patients with advanced NSCLC. The Phase 2 portion will evaluate administration at 400 mg/m ² on a three-week cycle, consisting of twice-weekly treatment for two weeks followed by one week off treatment. This treatment schedule, established in a

separate Phase 1 trial, provides a greater total dose of IPI-504 per treatment cycle and also has been equally well-tolerated. The time-off treatment is more convenient for patients and is not anticipated to adversely affect the potential for clinical benefit when compared to continuous treatment. Initial enrollment will total 20 patients (10 with and 10 without EGFR mutations), with additional patient enrollment triggered by continued evidence of clinical activity (i.e., partial response or stable disease greater than 12 weeks by RECIST).

Pre-Clinical Data in Her-2 Positive Breast Cancer

At the conference, the companies also presented research in which IPI-504 demonstrated evidence of preclinical activity in both Herceptin ^® (trastuzamab)-sensitive and -refractory Her-2 positive breast cancer cell lines. Her-2 (ErbB2) is expressed in a subset of metastatic breast cancers and is a client protein of Hsp90. In vivo , IPI-504, administered intravenously and orally on multiple schedules, demonstrated potent anti-proliferative effects against the cell lines examined, and dramatically induced the degradation of Her-2 and Akt in multiple cell lines.

“We are encouraged by the growing body of evidence suggesting the potential of Hsp90 inhibition to treat select forms of Her-2 positive cancers,” said Dirk Reitsma, MedImmune’s vice president, clinical development, oncology.

About IPI-504

IPI-504 is a small molecule drug candidate being developed jointly by Infinity and MedImmune. IPI-504 has been well-tolerated in its ongoing Phase 1 studies and has shown promising biological activity in Phase 1 clinical trials in patients with relapsed, refractory Gleevec ^® -resistant gastrointestinal stromal tumors and patients with advanced non-small cell lung cancer. In preclinical studies, IPI-504 has been shown to inhibit Hsp90 potently and selectively, thereby killing cancer cells. IPI-504 has also demonstrated, in preclinical studies, broad potential to treat certain cancers as both a single agent as well as in combination with existing anti-cancer drugs.

About Hsp90

Hsp90 is an emerging therapeutic target of interest for the treatment of cancer. Proteins are the mainstay of structural and signaling elements of all cells. Hsp90 is a molecule that maintains the conformation and activity of specific proteins in the cell — these proteins are known as “client proteins” of Hsp90. Many cancers result from specific mutations in, or aberrant expression of, these client proteins. Examples of oncogenic client proteins of Hsp90 include c-Kit in GIST, EGFR in NSCLC, and Bcr-Abl in chronic myelogenous leukemia. Hsp90 enables those cancers’ survival by maintaining the function of oncogenic client proteins. In preclinical studies, inhibition of Hsp90 has been shown to lead to the degradation of these proteins and cell death, or apoptosis. In addition, oncogenic client proteins that have become resistant to approved targeted therapies have also been shown preclinically to remain sensitive to Hsp90 inhibition. Inhibition of Hsp90 has broad therapeutic potential for the treatment of patients with solid tumors and blood-related cancers, including cancers that are resistant to other drugs.

About Non-Small Cell Lung Cancer

The American Cancer Society (ACS) reports that lung cancer is the leading cause of cancer death for both men and women. The ACS estimates that approximately 214,000 new cases of lung cancer will be diagnosed in the United States in 2007. According to the ACS, non-small cell lung cancer is the most common form of lung cancer, accounting for about 85 percent of all lung cancers. In some cases, specific mutations have been identified in a cellular signaling enzyme called epidermal growth factor receptor (EGFR). These mutations allow the survival signal of the mutated cancer cell to be switched “on” all the time. NSCLC patients with mutations in EGFR have been found to benefit from drugs such as Tarceva ^® and Iressa ^® that block EGFR signaling. Over time, however, resistance mutations develop such that patients become resistant to these agents. Mutated EGFR is a highly-sensitive client protein of Hsp90, suggesting that inhibition of Hsp90 in NSCLC is an attractive area for clinical study.

About PET Imaging and SUV _max

Positron emission tomography, also called PET, is an imaging technology that measures functional processes in the body. A radioactive isotope is attached to a metabolically active molecule related to glucose; the combined tracer molecule is then injected into the human body where it is taken up and trapped within the tumor cells. The most common tracer used in oncology for PET

imaging is 18-fluorodeoxyglucose, or 18-FDG. Different colors or degrees of brightness on a PET image represent different levels of tissue or organ metabolic activity. PET imaging in oncology takes advantage of the fact that cancer cells exhibit higher-than-normal levels of glucose uptake and, therefore, show up clearly as bright spots on PET images. Oncologists often use PET scans to detect tumors, or to examine the effects of a cancer therapy by measuring the metabolic activity of the cancer cell before and after treatment. Standardized Uptake Value (SUV) is a quantitative assessment of the metabolic activity of cells attained by PET imaging. SUV quantifies the ratio of uptake of a radioactive isotope, such as 18-FDG, for any given point in the body to the expected level. SUV _max measures SUV for the single point within a tumor lesion that has the highest SUV value. Tracking SUV _max for a single tumor lesion over time provides a standardized approach for assessing the decrease or increase in metabolic activity of the cancer during and after treatment by a cancer therapy. To date, 18-FDG PET imaging results and SUV _max have correlated with positive clinical outcomes in GIST patients treated with molecular targeted therapies.

About Infinity Pharmaceuticals, Inc.

Infinity is an innovative cancer drug discovery and development company that is seeking to leverage its strength in small molecule drug technologies to discover, develop, and deliver to patients best-in-class medicines for the treatment of cancer and related conditions. For more information on Infinity, please refer to the company’s website at http://www.ipi.com.

About MedImmune, Inc.

MedImmune strives to provide better medicines to patients, new medical options for physicians and rewarding careers to employees. With approximately 3,000 employees worldwide and headquarters in Maryland, MedImmune is dedicated to advancing science and medicine to help people live better lives and is wholly owned by AstraZeneca plc (LSE: AZN.L, NYSE: AZN). For more information, visit MedImmune’s website at http://www.medimmune.com.

Forward-Looking Statements

This announcement contains, in addition to historical information, certain forward-looking statements that involve risks and uncertainties, in particular statements related to the research and development of IPI-504 and other compounds targeting Hsp90. Such statements reflect the current views of MedImmune and/or Infinity management and are based on certain assumptions. MedImmune is a member of the AstraZeneca Group of companies. Actual results could differ materially from those currently anticipated as a result of a number of factors, including risks and uncertainties discussed in the reports and other documents filed by AstraZeneca plc with the Securities and Exchange Commission and in Infinity’s quarterly report on Form 10-Q for the quarter ended June 30, 2007 filed with the Securities and Exchange Commission on August 9, 2007. There can be no assurance that such development efforts will succeed, that the products will receive required regulatory clearance or, even if such regulatory clearance is received, that the subsequent products will ultimately achieve commercial success. Further, any forward-looking statements contained in this announcement speak only as of the date hereof, and AstraZeneca and Infinity expressly disclaim any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as otherwise may be required by applicable law or regulation.

Gleevec ^® , Tarceva ^® , Iressa ^® , and Herceptin ^® are registered trademarks of Novartis AG, OSI Pharmaceuticals, Inc., AstraZeneca UK Limited, and Genentech, Inc. respectively. INFI-G

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EXHIBIT 99.3

Steven H. Holtzman

115 Powers Road

Sudbury, Massachusetts 01776

Dear Steve:

Reference is made to your offer letter with Infinity Pharmaceuticals, Inc. (the “Company”) dated August 1, 2001 (the “Offer Letter”). It is understood and agreed that the following rules shall apply with respect to the distribution of the payments and benefits, if any, to be provided to you under Section 10 of the Offer Letter:

Please indicate your understanding and acceptance of the foregoing terms by countersigning this letter where indicated.

Acknowledged and agreed:

EXHIBIT 99.4

Julian Adams, Ph.D.

673 Boylston Street

Boston, Massachusetts 02116

Dear Julian:

Reference is made to your offer letter with Infinity Pharmaceuticals, Inc. (the “Company”) dated August 19, 2003 (the “Offer Letter”). It is understood and agreed that the following rules shall apply with respect to the distribution of the payments and benefits, if any, to be provided to you under Section 12 of the Offer Letter:

Please indicate your understanding and acceptance of the foregoing terms by countersigning this letter where indicated.

Acknowledged and agreed:

EXHIBIT 99.5

Adelene Q. Perkins

83 Lincoln Road

Wayland, Massachusetts 01778

Dear Adelene:

Reference is made to your offer letter with Infinity Pharmaceuticals, Inc. (the “Company”) dated February 6, 2002 (the “Offer Letter”). It is understood and agreed that the following rules shall apply with respect to the distribution of the payments and benefits, if any, to be provided to you under Section 11 of the Offer Letter:

Please indicate your understanding and acceptance of the foregoing terms by countersigning this letter where indicated.

Acknowledged and agreed: