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

                                  SCHEDULE 13G
                    Under the Securities Exchange Act of 1934
                                

                            Spectrum Pharmaceuticals
                                (Name of Issuer)

                                  Common Stock
                         (Title of Class of Securities)

                                    84763A108
                                 (CUSIP Number)

                                 September 15, 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.  84763A108


       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: 1,798,050
Beneficially
Owned by         7.  Sole Dispositive Power:  0
Each Reporting
Person With      8.  Shared Dispositive Power: 1,798,050

       9.    Aggregate Amount Beneficially Owned by Each Reporting Person
             1,798,050

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

       11.   Percent of Class Represented by Amount in Row (9) 8.22%

       12.   Type of Reporting Person (See Instructions) IA






                               CUSIP No.  84763A108


       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: 1,059,093
Beneficially
Owned by         7.  Sole Dispositive Power: 0
Each Reporting
Person With      8.  Shared Dispositive Power:  1,059,093

       9.    Aggregate Amount Beneficially Owned by Each Reporting Person
             1,059,093

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

       11.   Percent of Class Represented by Amount in Row (9) 4.84%

       12.   Type of Reporting Person (See Instructions) IA




                               CUSIP No.  84763A108


       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: 2,857,143
Beneficially
Owned by         7.  Sole Dispositive Power: 0
Each Reporting
Person With      8.  Shared Dispositive Power: 2,857,143

       9.    Aggregate Amount Beneficially Owned by Each Reporting Person:
             2,857,143

       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: Spectrum Pharmaceuticals

             1.      Address:
                     157 TECHNOLOGY DR
		     IRVINE CA 92618 



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:  84763A108

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 (589,062 shares and
         294,531 warrants), Caduceus Capital II, L.P. (306,000 shares
         and 153,000 warrants), UBS Eucalyptus Fund, LLC (500,000 shares and
         250,000 warrants), PaineWebber Eucalyptus Fund, LLC (50,000 shares
         and 25,000 warrants), HFR SHC Aggressive Fund (117,000 shares and
	 58,500 warrants), Knightsbridge Post Venture IV L.P. (71,000 shares
	 and 35,500 warrants), Knightsbridge Integrated Holdings, V, LP 
         (79,000 shares and 39,500 warrants),Knightsbridge Netherlands II, 
         LP (20,000 shares and 10,000 warrants), Knightsbridge 
	 Integrated Holdings IV Post Venture, LP (30,000 shares and
         15,000 warrants), Knightsbridge Post Venture III, LP (19,500 shares
         and 9,750 warrants), Knightsbridge Netherlands I LP (18,800 shares
         and 9,400 warrants), Knightsbridge Netherlands III LP
         (19,300 shares and 9,650 warrants), Knightsbridge Integrated 
         Holdings II Limited (24,500 shares and 12,250 warrants), 
         Knightsbridge Venture Completion 2005 LP (7,500 shares and 3,750
	 warrants), and Knightsbridge Venture Capital VI LP (20,300 shares and
         10,150 warrants), Knightsbridge Venture Capital IV LP (19,200 shares
         and 9,600 warrants), and Knightsbridge Venture Capital III LP
         (13,600 shares and 6,800 warrants).

			**Blocker Provision


Holder's Restrictions.  The Holder shall not have the right to exercise
any portion of this Warrant to the extent that after giving effect to 
such issuance after exercise, the Holder (together with the Holder's 
affiliates), as set forth on the applicable Notice of Exercise, would 
beneficially own in excess of 9.99% of the number of shares of the 
Common Stock outstanding immediately after giving effect to such 
issuance (such limitation being referred to herein as the "Beneficial 
Ownership Cap").  For purposes of the Beneficial Ownership Cap, the 
number of shares of Common Stock beneficially owned by the Holder 
and its affiliates shall include the number of shares of Common 
Stock issuable upon exercise of this Warrant with respect to which 
the determination of such sentence is being made, but shall exclude 
the number of shares of Common Stock which would be issuable upon 
(A) exercise of the remaining, nonexercised portion of this Warrant 
beneficially owned by the Holder or any of its affiliates and (B) 
exercise or conversion of the unexercised or nonconverted portion 
of any other securities of the Company (including, without limitation, 
any other Shares or Warrants) subject to a limitation on conversion or 
exercise analogous to the Beneficial Ownership Cap beneficially owned 
by the Holder or any of its affiliates.  Except as set forth in the 
preceding sentence, for purposes of this Section 2(c), beneficial 
ownership shall be calculated in accordance with Section 13(d) of 
the Exchange Act, it being acknowledged by Holder that the Company 
is not representing to Holder that such calculation is in compliance 
with Section 13(d) of the Exchange Act and Holder is solely responsible 
for any schedules required to be filed in accordance therewith.   
To the extent that the Beneficial Ownership Cap applies, the 
determination of whether this Warrant is exercisable (in relation to 
other securities owned by the Holder) and of which a portion of this 
Warrant is exercisable shall be in the sole discretion of such Holder, 
and the submission of a Notice of Exercise shall be deemed to be such 
Holder's representation to the Company that its Warrant is exercisable 
(in relation to other securities owned by such Holder) and of which 
portion of this Warrant is exercisable, in each case subject to such 
aggregate percentage limitation, and the Company shall have no 
obligation to verify or confirm the accuracy of such determination.  
For purposes of this Section 2(d), in determining the number of 
outstanding shares of Common Stock, the Holder may rely on the number 
of outstanding shares of Common Stock as reflected in (x) the Company's 
most recent Form 10-Q or Form 10-K, as the case may be, (y) a more recent 
public announcement by the Company or (z) any other notice by the Company
or the Company's Transfer Agent setting forth the number of shares of 
Common Stock outstanding.  Upon the written or oral request of the Holder, 
the Company shall within two Trading Days confirm orally and in writing 
to the Holder the number of shares of Common Stock then outstanding.  
In any case, the number of outstanding shares of Common Stock shall be 
determined after giving effect to the conversion or exercise of securities 
of the Company, including this Warrant, by the Holder or its affiliates 
since the date as of which such number of outstanding shares of Common 
Stock was reported. 




         
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: September 21, 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
September 21, 2005, (the "Schedule 13G"), with respect to the Common Stock, par 
value $.001 per share, of Spectrum Pharmaceuticals 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 21st day of Sepember, 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 September 21, 2005 with respect to the 
common stock, $.001 par value per share, of Spectrum Pharmaceuticals 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).