Immunogen (IMGN) 8-K Results of Operations and Financial Condition

Exhibit 99.1

T A R G E T A B E T T E R N O W Nasdaq: IMGN Corporate Presentation As of January 13, 2020 Exhibit 99.1

2 FORWARD-LOOKING STATEMENTS This presentation includes forward-looking statements regarding ImmunoGen’s expectations related to the design and potential success of ImmunoGen’s future mirvetuximab soravtansine and IMGN632 clinical studies and regulatory pathways, including the timing of initiating and receiving data from, as well as the likelihood of success of, the planned registration studies of mirvetuximab; the occurrence, timing, and outcome of other potential preclinical, clinical, and regulatory events related to ImmunoGen’s and its collaboration partners’ programs; and potential future collaborations. For these statements, ImmunoGen claims the protection of the safe harbor for forward-looking statements provided by the Private Securities Litigation Reform Act of 1995. Various factors could cause ImmunoGen’s actual results to differ materially from those discussed or implied in the forward-looking statements, and you are cautioned not to place undue reliance on these forward-looking statements, which are current only as of the date of this presentation. Factors that could cause future results to differ materially from such expectations include, but are not limited to, the risks and uncertainties inherent in the Company’s development programs, including clinical studies and regulatory processes, their timings and results, including the possibility that future studies of mirvetuximab fail to confirm the hypotheses suggested by the exploratory analyses of the FORWARD I data.A review of these risks can be found under the heading “Risk Factors” in ImmunoGen’s Annual Report on Form 10-K for the year ended December 31, 2018 and subsequent documents filed with the Securities and Exchange Commission.

3 WHY IMMUNOGEN? ACCELERATED P A T H T O PIVOTAL DATA IN 2021 AND APPROVAL IN 2022 ROBUST DATA I N L E A D MIRVETUXIMAB PROGRAM STRONG CASH POSITION D I V E R S E PORTFOLIO OF EARLY STAGE P R O D U C T CANDIDATES ANTICIPATED C O M P E N D I A LISTING FOR FOLLOW- O N INDICATIONS BEGINNING I N 2 0 2 2 ACCELERATED P A T H T O PIVOTAL DATA IN 2021 AND P O T E N T I A L APPROVAL I N 2 0 2 2

4 BRINGING ANTIBODY - DRUG CONJUGATES TO CANCER PATIENTS STRATEGIC PRIORITIES F U R T H E R STRENGTHEN BALANCE SHEET AND EXPAND CAPABILITIES T H R O U G H PARTNERSHIPS ADVANCE PORTFOLIO OF EARLY STAGE P R O D U C T CANDIDATES E X E C U T E MIRVETUXIMAB REGISTRATION STUDIES AND PURSUE LABEL EXPANSION

SOMEONE YOU KNOW HAS BEEN DIAGNOSED WITH OVARIAN CANCER … WHAT’S NEXT FOR HER? 5

U R G E N T NEED 1NIH SEER Data: Estimated New Cases, 2019. 2JCO: Vol 33, No. 32, Nov 2015. 3Gyn Onc 133(2014) 624-631. PFS: progression-free survival; PARPi: poly-ADP ribose polymerase inhibitor; BEV: bevacizumab OVARIAN CANCER IS THE LEADING CAUSE OF DEATH FROM GYNECOLOGICAL CANCERS >14,000 WOMEN DIE ANNUALLY FROM OVARIAN CANCER IN US1 6 DISEASE PROGRESSION WITHIN 6 MONTHS AFTER PLATINUM TREATMENT PLATINUM- RESISTANT PLATINUM- B A S E D CHEMOTHERAPY +/- P A R P i /BEV MAINTENANCE PLATINUM-SENSITIVE DISEASE PROGRESSION MORE THAN 6 MONTHS AFTER PLATINUM TREATMENT SURGERY DIAGNOSIS ~22,500 WOMEN DIAGNOSED ANNUALLY 1 MOST PATIENTS DEVELOP PLATINUM - RESISTANT DISEASE: LIMITED OPTIONS WITH POOR OUTCOMES • Low response rates and short PFS with current single agents2, 3 • Significant toxicities associated with current treatments2, 3

MIRVETUXIMAB SORAVTANSINE 7 DESIGNED TO DISPLACE CHEMOTHERAPY TO DELIVER MORE GOOD DAYS FOR WOMEN WITH OVARIAN CANCER KEY ATTRIBUTES • ADC with distinct FRα target and mechanism of action • Demonstrated activity in patients with platinum-resistant and platinum-sensitive ovarian cancer1 • Well tolerated with differentiated safety profile • Potential in other FRα-positive solid tumors DEVELOPMENT STRATEGY • Seek initial label as monotherapy in platinum-resistant ovarian cancer • Pursue combinations with approved agents to expand into earlier lines of therapy • Lever cooperative groups and ISTs to generate complementary data 1ASCO 2017 Poster; Moore K., et. al. FRα: folate receptor alpha; IST: investigator sponsored trial

8 ALIGNED WITH FDA RECOMMENDATIONS WOMEN WITH FRα -H I G H PLATINUM-R E S I S T A N T OVARIAN CANCER THAT HAS PROGRESSED AFTER PRIOR TREATMENT WITH BEVACIZUMAB REQUIRE BETTER THERAPEUTIC OPTIONS MIRVETUXIMAB: POTENTIAL FOR ACCELERATED APPROVAL SUPPORTING DATA POOLED POST-HOC ANALYSIS FROM PHASE 1 AND FORWARD I STUDIES BEVACIZUMAB PRE-TREATED PATIENTS Using PS2+ Scoring Method, 1-3 Priors, n=70 31.4% ORR 95% CI (20.9%, 43.6%) 7.8 mos mDOR 95% CI (3.98, --) WE BELIEVE REPLICATING THESE DATA IN A SINGLE-ARM STUDY COULD SUPPORT ACCELERATED APPROVAL 1AVASTIN prescribing information. 2ESMO 2018; Gaillard S., et. al. ORR: confirmed overall response rate; mDOR: median duration of response CI: confidence interval 8 12% ORR EXPECTATION FOR BEST AVAILABLE THERAPIES1,2

9 SINGLE-ARM PIVOTAL TRIAL FOR MIRVETUXIMAB USING PS2+ SCORING IN FRα-HIGH, PLATINUM-RESISTANT OVARIAN CANCER PRIMARY ENDPOINT ORR by Investigator SECONDARY ENDPOINT DOR by Investigator FPI Q1 2020 TARGET TIMELINES ENROLLMENT AND KEY ELIGIBILITY ~100 patients Platinum-resistant disease (primary PFI >3 mos) Prior bevacizumab required Prior PARPi allowed Patients with BRCA mutations allowed TOPLINE DATA MID 2021 BLA H2 2021 FPI: first patient in; DOR: duration of response; PFI: platinum-free interval

10 PRIOR PHASE 3 EXPERIENCE FORWARD I DID NOT MEET PRIMARY ENDPOINT GENERATED ROBUST DATA TO INFORM POTENTIAL REGISTRATION PHYSICIAN’S CHOICE OF PACLITAXEL, PLD, OR TOPOTECAN MIRVETUXIMAB 2:1 RANDOMIZATION PRIMARY ENDPOINT PFS for all patients and for FRα-high expressers only ENROLLMENT 366 patients with FRα-positive* (med/high) platinum-resistant ovarian cancer treated with up to 3 prior regimens SAFETY1 WELL TOLERATED WITH A DIFFERENTIATED PROFILE Safety data demonstrated predominantly low grade drug-related adverse events. Compared to chemo, mirvetuximab was associated with: Fewer Grade ≥3 TEAEs Fewer dose reductions due to related TEAEs Fewer discontinuations due to related TEAEs EFFICACY1 OUTCOMES CORRELATED WITH FRα EXPRESSION Compared to chemo, in FRα-high patients, mirvetuximab was associated with: Longer PFS Higher confirmed ORR Longer OS 1ESMO 2019 Moore K., et. al. *FRα scoring by 10X. PLD: pegylated liposomal doxorubicin; TEAEs: treatment emergent adverse events; OS: overall survival

11 APPLYING LESSONS LEARNED FROM FORWARD I WE BELIEVE THESE DESIGN FACTORS WILL IMPROVE THE PROBABILITY OF TECHNICAL SUCCESS FOR MIRASOL DESIGN FACTOR INSIGHT 11 n=366 n=430 FRα-highs benefited most PS2+ reliably identified patients most likely to benefit Efficient, conservative design Preserves alpha for primary endpoint Acceptable as primary endpoint; aligns with real- world practice HR: hazard ratio; BICR: Blinded Independent Central Review; INV: investigator FRα- medium and high FRα- high only Patient Population FRα by 10X FRα by PS2+ Patient Selection HR of 0.58 with 2:1 design HR of 0.70 with 1:1 design Statistical Design Hochberg with split alpha No split alpha Statistical Design PFS by BICR PFS by INV Primary Endpoint Assessment

12 ENROLLMENT AND KEY ELIGIBILITY • 430 patients/330 events for PFS by Investigator • Platinum-resistant disease (primary PFI >3 mos) • Prior bevacizumab allowed* • Prior PARPi allowed • Patients with BRCA mutations allowed Mirvetuximab PHASE 3 RANDOMIZED TRIAL FOR MIRVETUXIMAB USING PS2+ SCORING IN FRα-HIGH, PLATINUM- RESISTANT OVARIAN CANCER PRIMARY ENDPOINT PFS by Investigator BICR for Sensitivity Analysis *Eligibility criterion different than SORAYA IC: investigator’s choice; PRO: patient reported outcomes SECONDARY ENDPOINTS ORR by Investigator, OS, and PRO Investigator’s Choice Chemotherapy Paclitaxel, PLD, or T o p o t e c a n STRATIFICATION FACTORS IC Chemotherapy (Paclitaxel, PLD, Topotecan) Prior Therapies (1 vs 2 vs 3) 1:1 RANDOMIZATION

13 PLATINUM-RESISTANTPLATINUM-SENSITIVE MIRVETUXIMAB + BEVACIZUMAB1 Median Number of Prior Therapies (Range): 3 (1-8) MIRVETUXIMAB + CARBOPLATIN2 Median Number of Prior Therapies (Range): 2.5 (1-6) FRα-HIGH1 (n=28) AURELIA-TYPE (n=16) FRα-MED + FRα-HIGH1 (n=10) 39% ORR 56% ORR 80% ORR 7.1 mos mPFS 9.9 mos mPFS 15.0 mos mPFS 1ASCO 2019 Poster; O’Malley D., et al. 2Gynecologic Oncology 151 (2018) 46-52. 3AVASTIN prescribing information. 4Aghajanian, et al., JCO 30:2039 (2012). 5Coleman, et al., Lancet Oncology 18:779 (2017). GOAL: BECOME COMBINATION AGENT OF CHOICE IN OVARIAN CANCER MIRVETUXIMAB LABEL EXPANSION • Favorable safety data; adverse events in line with known profiles of bevacizumab and carboplatin • Full doses of bevacizumab1 and carboplatin2 combined with full dose mirvetuximab were well tolerated • Additional platinum-agnostic bevacizumab expansion cohort fully enrolled in September 2019; data anticipated mid-2020 • Additional platinum-sensitive doublet to initiate in early 2020 FORWARD II OUTCOMES COMPARE FAVORABLY TO COMPETITIVE BENCHMARKS 3 , 4 , 5

14 2020 DRUG TREATABLE RECURRENT OVARIAN CANCER PATIENTS 2L 3L PLANTINUM - RESISTANT 10k PLANTINUM - SENSITIVE 2k 2L 3L 4L 2L 3L 5k 9k 8k ~50% SINGLE AGENT CHEMO ~50% SINGLE AGENT CHEMO *Numbers represent Company estimates of US patients with conditions covered by the Company’s targeted indications. Sources: Decision Resources Group, diagnosed drug-treatable patients 2020. Kantar Health. Ipsos Oncology Monitor; average Q4 2018 – Q3 2019. ImmunoGen market research. ~60% SINGLE AGENT CHEMO

15 MIRVETUXIMAB MARKET OPPORTUNITY FIRST TARGETED INDICATION AND ADDITIONAL EXPANSION INDICATIONS WOULD ADDRESS KEY SEGMENTS OF RECURRENT OVARIAN CANCER MARKET 2L 3L PLANTINUM - RESISTANT 10k PLANTINUM - SENSITIVE 2k 2L 3L 4L 2L 3L 5k 9k 8k FIRST TARGETED INDICATION: MONOTHERAPY 2L- 4L PLATINUM -RESISTANT POTENTIAL FOR Accelerated Approval in 2022 Full Approval in 2023 ~5,000 FRα -HIGH PATIENTS ADDITIONAL EXPANSION INDICATION: M I R V + B E V PLATINUM-AGNOSTIC POTENTIAL FOR Compendia Listing in 2022 ~2,300 FRα -HIGH PATIENTS ADDITIONAL EXPANSION INDICATION: MIRV + CARBO PLATINUM-SENSITIVE POTENTIAL FOR Compendia Listing in 2022 ~2,300 FRα -HIGH PATIENTS OTHER ~50% SINGLE AGENT CHEMO ~25% BEV COMBO ~20% BEV COMBO ~50% SINGLE AGENT CHEMO ~60% SINGLE AGENT CHEMO ~15% BEV COMBO ~50% PLAT COMBO1 OTHER ~10% BEV COMBO 2 OTHER OTHER OTHER ~10% BEV COMBO2 ~40% PLAT COMBO1 *Numbers represent Company estimates of US patients with conditions covered by the Company’s targeted indications. 1Regimens that incorporate platinum including bevacizumab combinations. 2Non-platinum regimens. Sources: Decision Resources Group, diagnosed drug-treatable patients 2020. Kantar Health. Ipsos Oncology Monitor; average Q4 2018 – Q3 2019. ImmunoGen market research.

16 ROBUST DATA • Strong and consistent efficacy signals observed in FRα-high patients • Favorable tolerability • PS2+ reliably identified patients most likely to benefit SORAYA: POTENTIAL PATH TO ACCELERATED APPROVAL • Enroll first patient in Q1 2020 • Topline data expected in mid-2021; BLA expected in H2 2021 • Potential for accelerated approval in 2022 MIRASOL: DESIGNED TO PROVIDE DATA TO SUPPORT FULL APPROVAL • Now enrolling patients • Topline data expected in H1 2022 • Potential for full approval in 2023 COMBINING TO DEVELOP MIRVETUXIMAB FOR EARLIER LINES OF THERAPY • Platinum-agnostic cohort fully enrolled; data expected in mid-2020 • Additional platinum-sensitive doublet to initiate in early 2020 • Exploring additional pathways to label expansion MIRVETUXIMAB P R O G R A M SUMMARY

17 • More than 10,000 deaths due to AML in US each year1 • 5-year overall survival is ~25%1 • Median overall survival is ~6 months in relapsed/refractory AML2-3 C H E M O + TARGETED THERAPY STEM CELL TRANSPLANT DIAGNOSIS ~ 21,500 NEW CASES DIAGNOSEDANNUALLY 1 CHEMOTHERAPY U R G E N T NEED SELECT CASES SELECT CASES 17 SOMEONE YOU KNOW HAS BEEN DIAGNOSED WITH ACUTE MYELOID LEUKEMIA… WHAT’S NEXT? 1NIH SEER Data; Estimated New Cases, 2019. 2Faderl, S., et al. J Clin Oncol 2012; 30:2492-2499. 3Ravandi, F., et al. Lancet Oncol 2015; 16:1025-36. AML: acute myeloid leukemia

I M G N 6 3 2 18 DESIGNED TO TARGET MULTIPLE CD123+ HEMATOLOGIC MALIGNANCIES KEY ATTRIBUTES • CD123-targeted ADC with novel DNA-acting payload • Demonstrated activity with complete responses in AML and BPDCN1 • Favorable safety observed at multiple dose levels1 DEVELOPMENT STRATEGY • Fast-to-market in BPDCN patients • Potential label expansion: monotherapy in frontline MRD+ AML; in combination for relapsed AML and frontline AML patients unfit for intensive induction chemotherapy • Seek proof of concept in additional CD123-positive heme malignancies including ALL 1ASH 2018 Oral Presentation; Daver D., et al. BPDCN: blastic plasmacytoid dendritic cell neoplasm; MRD: minimal residual disease; ALL: acute lymphoblastic leukemia

19 I M G N 6 3 2 ADVANCING EXPANSION COHORTS • Recommended Phase 2 dose and schedule identified • Monotherapy and combination trials enrolling – Monotherapy: BPDCN and frontline MRD+ AML – Doublet: with azacitidine and with venetoclax in r/r AML – Triplet: with azacitidine and venetoclax in AML • Expansion data expected at ASH 2020 SAFETY • Well tolerated at multiple dose levels, including the recommended Phase 2 dose and schedule • Manageable infusion-related reactions, none requiring discontinuation • Most doses given as outpatient with <30 minute infusion every three weeks r/r AML • 26-46% ORR in r/r AML at the recommended Phase 2 dose in subgroups of patients with relapsed disease • Majority of responders were ELN adverse risk with 2-3 prior lines of therapy, including three with prior SCT BPDCN • Responses in 3 of 9 patients, all with prior SL-401 and two with intense chemotherapy 1ASH 2019 IMGN632 Oral Presentation; Daver D., et al. ELN: European LeukemiaNet; SCT: stem cell transplant ASH 2019 CONCLUSIONS1 ENCOURAGING CLINICAL PROFILE OF IMGN632 IN PATIENTS WITH R/R AML OR BPDCN 19

20 ADVANCING A SELECT PORTFOLIO OF EARLY STAGE PRODUCT CANDIDATES • First-in-class ADAM9-targeting therapy • ADAM9 is overexpressed in multiple solid tumors (e.g., NSCLC, gastric, pancreatic, TNBC) 1 • Comprised of high-affinity humanized antibody with YTE mutation conjugated to DM21, a next-generation maytansinoid payload combined with a stable peptide linker • 50/50 co-development; MacroGenics IND submission expected in first half of 2020 • Next-generation anti-FRα ADC designed to have improved activity against lower FRα-expressing tumors • Combines advances in antibody engineering and new payload technology • Transition to preclinical development anticipated in 2020 CONTINUED INNOVATION GENERATING DIFFERENTIATED ADCs IMGC936 IMGN151 20 1AACR 2019 Poster; Hicks S., et al. NSCLC: non-small cell lung cancer; TNBC: triple-negative breast cancer

EVOLVING OUR APPROACH TO PARTNERING CO- OWNERSHIP AND MONETIZATION OF ASSETS TO STRENGTHEN BALANCE SHEET 21 LEGACY PLATFORM DEALS

22 THE NEXT 12 MONTHS OUR PATH TO SUCCESS MIRVETUXIMAB SORAVTANSINE • Open pivotal SORAYA trial in Q1 2020 • Enroll patients in confirmatory MIRASOL trial • Initiate additional platinum-sensitive combination in early 2020 • Present initial data from FORWARD II platinum-agnostic and updated triplet combination studies in mid-2020 I M G C 9 3 6 • IND submission by MacroGenics anticipated in the first half of 2020 I M G N 6 3 2 • Continue enrollment in expansion cohorts • Present AML combo and BPDCN and MRD+ monotherapy data at ASH 2020 I M G N 1 5 1 • Transition to preclinical development in mid-2020

ROBUST DATA IN LEAD MIRVETUXIMAB PROGRAM ACCELERATED PATH TO PIVOTAL DATA IN 2021 AND POTENTIAL APPROVAL IN 2022 IMGN632 ADVANCING INTO EXPANSION DIVERSE PORTFOLIO OF EARLY STAGE PRODUCT CANDIDATES STRONG CASH POSITION ANTICIPATED COMPENDIA LISTING FOR FOLLOW - O N INDICATIONS BEGINNING IN 2022