UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G
                    Under the Securities Exchange Act of 1934
                                

                        	  Cytogen Corp.
                                (Name of Issuer)

                                  Common Stock
                         (Title of Class of Securities)

                                    232824300
                                 (CUSIP Number)

                                 July 19, 2005

             (Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule
is filed:

[x] Rule 13d-1(b)

[ ] Rule 13d-1(c)

[ ] Rule 13d-1(d)

*The remainder of this cover page shall be filled out for a reporting person's
initial filing on this form with respect to the subject class of securities, and
for any subsequent amendment containing information which would alter the
disclosures provided in a prior cover page.


The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the Securities Exchange Act of
1934 ("Act") or otherwise subject to the liabilities of that section of the Act
but shall be subject to all other provisions of the Act (however, see the
Notes).




                               CUSIP No.  232824300


       1.    Names of Reporting Persons.
             I.R.S. Identification Nos. of above persons (entities only).

             OrbiMed Advisors LLC

       2.    Check the Appropriate Box if a Member Of a Group (See Instructions)

             [ ] (a)
             [ ] (b)

       3.    SEC Use Only

       4.    Citizenship or Place of Organization

             Delaware

       5.    Sole Voting Power: 0
Number of
Shares           6.  Shared Voting Power: 1,287,573
Beneficially
Owned by         7.  Sole Dispositive Power:  0
Each Reporting
Person With      8.  Shared Dispositive Power: 1,287,573

       9.    Aggregate Amount Beneficially Owned by Each Reporting Person
             1,287,573

       10.   Check if the Aggregate Amount in Row (9) Excludes Certain Shares
             (See Instructions)

       11.   Percent of Class Represented by Amount in Row (9) 6.67%

       12.   Type of Reporting Person (See Instructions) IA






                               CUSIP No.  232824300


       1.    Names of Reporting Persons.
             I.R.S. Identification Nos. of above persons (entities only).

             OrbiMed Capital LLC

       2.    Check the Appropriate Box if a Member of a Group (See Instructions)

             [ ] (a)
             [ ] (b)

       3.    SEC Use Only

       4.    Citizenship or Place of Organization

             Delaware

       5.    Sole Voting Power: 0
Number of
Shares           6.  Shared Voting Power: 914,487
Beneficially
Owned by         7.  Sole Dispositive Power: 0
Each Reporting
Person With      8.  Shared Dispositive Power:  914,487

       9.    Aggregate Amount Beneficially Owned by Each Reporting Person
             914,487

       10.   Check if the Aggregate Amount in Row (9) Excludes Certain Shares
             (See Instructions)

       11.   Percent of Class Represented by Amount in Row (9) 4.74%

       12.   Type of Reporting Person (See Instructions) IA




                               CUSIP No.  232824300


       1.    Names of Reporting Persons.
             I.R.S. Identification Nos. of above persons (entities only).

             Samuel D. Isaly

       2.    Check the Appropriate Box if a Member of a Group (See Instructions)

             [ ] (a)
             [ ] (b)

       3.    SEC Use Only

       4.    Citizenship or Place of Organization

             United States

       5.    Sole Voting Power: 0
Number of
Shares           6.  Shared Voting Power: 1,910,817
Beneficially
Owned by         7.  Sole Dispositive Power: 0
Each Reporting
Person With      8.  Shared Dispositive Power: 1,910,817

       9.    Aggregate Amount Beneficially Owned by Each Reporting Person:
             1,910,817

       10.   Check if the Aggregate Amount in Row (9) Excludes Certain Shares
             (See Instructions)

       11.   Percent of Class Represented by Amount in Row (9) 9.99%

       12.   Type of Reporting Person (See Instructions) HC




Item 1. (a)  Issuer: Cytogen Corp.

             1.      Address:
                     650 COLLEGE RD EAST STE 3100
		     PRINCETON NJ 08540 


Item 2. (a)  Name of Person Filing:
             OrbiMed Advisors LLC
             OrbiMed Capital LLC
             Samuel D. Isaly

        (b)  Address of Principal Business Offices:

             767 Third Avenue, 30th Floor
             New York, New York 10017

        (c)  Citizenship:
             Please refer to Item 4 on each cover sheet for each filing person

        (d)  Title of Class of Securities
             Common stock

        (e)  CUSIP Number:  232824300

Item 3. OrbiMed Advisors LLC and OrbiMed Capital LLC are investment advisors in
accordance with ss.240.13d-1(b)(1)(ii)(E). Samuel D. Isaly is a control person
in accordance with ss.240.13d-1(b)(1)(ii)(G).

Item 4.  Ownership

         Please see Items 5 - 9 and 11 for each cover sheet for each filing
separately

Item 5.  Ownership of Five Percent or Less of a Class

         Not Applicable


Item 6.  Ownership of More than Five Percent on Behalf of Another Person.

	 Reporting persons are holding 9.99% of the securities on behalf of 
         other persons who have the right to receive or the power to direct 
         the receipt of dividends from, or proceeds from sale of, such 
	 securities. No one such other person's interest in the securities 
	 whose ownership is reported here relates to more than five percent 
         of the class.

         OrbiMed Advisors LLC and OrbiMed Capital LLC hold shares on
         behalf of Caduceus Capital Master Fund Limited (600,000 shares and
         150,000 warrants), Caduceus Capital II, L.P. (300,000 shares
         and 75,000 warrants), UBS Eucalyptus Fund, LLC (460,000 shares and
         115,000 warrants), PaineWebber Eucalyptus Fund, LLC (50,500 shares
         and 12,500 warrants), HFR SHC Aggressive Fund (117,190 shares and
	 47,297 warrants), Knightsbridge Post Venture IV L.P. (60,900 
	 warrants), Knightsbridge Integrated Holdings, V, LP (49,673 warrants), 
         Knightsbridge Netherlands II, LP (19,700 warrants), Knightsbridge 
	 Integrated Holdings IV Post Venture, LP (36,000 warrants),
         Knightsbridge Post Venture III, LP (35,400 warrants), Knightsbridge
         Netherlands I LP (22,100 warrants), Knightsbridge Netherlands III LP
         (5,600 warrants), Knightsbridge Integrated Holdings II Limited
	 (37,700 warrants), Knightsbridge Venture Capital IV, L.P. (5,600 
	 warrants), and Knightsbridge Venture Capital III LP (2,400 warrants).

			Blocker Provision


Notwithstanding anything to the contrary contained herein, the number of shares 
of Common Stock that may be acquired by the Registered Holder upon any exercise 
of this Warrant (or otherwise in respect hereof) shall be limited to the extent 
necessary to insure that, following such exercise (or other issuance), the total
number of shares of Common Stock then beneficially owned by such Registered 
Holder and its Affiliates (as defined in the SPA) and any other Persons (as 
defined in the SPA) whose beneficial ownership of Common Stock would be 
aggregated with the Holder's for purposes of Section 13(d) of the Exchange Act,
does not exceed 9.999% of the total number of issued and outstanding shares of 
Common Stock (including for such purpose the shares of Common Stock issuable 
upon such exercise). For such purposes, beneficial ownership shall be 
determined in accordance with Section 13(d) of the Exchange Act (as defined 
in the SPA) and the rules and regulations promulgated thereunder.  Each 
delivery of a purchase form hereunder will constitute a representation by the 
Registered Holder that it has evaluated the limitation set forth in this 
paragraph and determined that issuance of the full number of Warrant Shares 
requested in such purchase form is permitted under this paragraph.  This 
provision shall not restrict the number of shares of Common Stock which a 
Registered Holder may receive or beneficially own in order to determine 
the amount of securities or other consideration that such Registered Holder
may receive in the event of a merger or other business combination or 
reclassification involving the Company as contemplated in Section 
2(e) of this Warrant.  This restriction may not be waived.



         
Item 7.  Identification and Classification of the Subsidiary Which Acquired the
Security  Being Reported on By the Parent Holding Company

         Not Applicable

Item 8.  Identification and Classification of Members of the Group

         Not Applicable


Item 9.  Notice of Dissolution of Group

         Not Applicable

Item 10. Certification

         By signing below I certify that, to the best of my knowledge and
belief, the securities referred to above were acquired and held in the ordinary
course of business and were not acquired and are not held for the purpose of or
with the effect of changing or influencing the control of the issuer of the
securities and were not acquired and are not held in connection with or as a
participant in any transaction having that purpose or effect.





                                    SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify
that the information set forth in this statement is true, complete and correct.

Date: August 3, 2005
                                       OrbiMed Advisors LLC

                                       By: /s/ Samuel D. Isaly
                                       --------------------------
                                       Name:  Samuel D. Isaly
                                       Title: President

                                       OrbiMed Capital LLC

                                       By: /s/ Samuel D. Isaly
                                       --------------------------
                                       Name:  Samuel D. Isaly
                                       Title: Managing Member


                                       By: /s/ Samuel D. Isaly
                                       --------------------------
                                       Name:  Samuel D. Isaly
			

			JOINT FILING AGREEMENT

The undersigned hereby agree that the Statement on this Schedule 13G, dated
August 3, 2005, (the "Schedule 13G"), with respect to the Common Stock, par 
value $.001 per share, of Cytogen Corp. is filed on behalf of each of us 
pursuant to and in accordance with the provisions of Rule 13d-1(k) under the 
Securities and Exchange Act of 1934, as amended, and that this Agreement shall 
be included as an Exhibit to this Schedule 13G. Each of the undersigned agrees 
to be responsible for the timely filing of the Schedule 13G, and for the 
completeness and accuracy of the information concerning itself contained 
therein. This Agreement may be executed in any number of counterparts, all of 
which taken together shall constitute one and the same instrument.

        IN WITNESS WHEREOF, the undersigned have executed this Agreement as of
the 3rd day of August, 2005.


                                          OrbiMed Advisors LLC

                                          By: /s/ Samuel D. Isaly
                                          ---------------------------
                                          Name:  Samuel D. Isaly
                                          Title: Managing Member


                                          OrbiMed Capital LLC

                                          By: /s/ Samuel D. Isaly
                                          ----------------------------
                                          Name:  Samuel D. Isaly
                                          Title: Managing Member


                                          By: /s/ Samuel D. Isaly
                                          ----------------------------
                                          Name:  Samuel D. Isaly


				


				
				Statement of Control Person


The Statement on this Schedule 13G dated August 3, 2005 with respect to the 
common stock, $.001 par value per share, of Cytogen Corp. is filed by 
Samuel D. Isaly in accordance with the provisions of Rule 13d-1(b) and Rule 
13d-1(k),respectively, as control person (HC) of OrbiMed Advisors LLC and 
OrbiMed Capital LLC.

OrbiMed Advisors LLC and OrbiMed Capital LLC file this statement on Schedule 13G
in accordance with the provisions of Rule 13d-1(b) and Rule 13d-1(k),
respectively, as investment advisors (IA).