The survival curve on the left conceals a remarkable epidemiological feature of cancer, the bi-modal hazard rate (BMH), depicted on the right side. †Its significance† is explained elsewhere

The curve proceeds through three phases:
1. Hazard rises due to treatment (AB segment)
2. Hazard declines and the patientís prospect† improves (BC segment).
3. Final deterioration and death (CD segment)

 We are concerned here with the ascending phase (AB), while the significance of the descending phase (BC) is discussed elsewhere.

The rising hazard rate following treatment indicates that the† patient depends somehow on her tumor and its removal  raises the hazard rate. In rare occasions this phenomenon may be observed also in †survival curves. The survival curves depicted below were published by Cronin et al (1) †and modified slightly, e.g. adding the arrows and letters to highlight the present argument.

Fig. 2. Cause-specific survival for women diagnosed with breast cancer between 1975 and 1979 in the Surveillance, Epidemiology, and End Results (SEER) 9 regions by age and historical stage. Cronin et al (1).

Tumor dependency is most pronounced in the 30-39 age group (red).

The survival of patients with local disease is worse than that observed in other ages. The difference between the red survival curve and the other will be called here survival deficit. In young females with local disease the survival deficit is the largest (A). Females with regional cancer start with a positive survival deficit (B). By the 10th year it becomes negative (C). Females with regional cancers have a negative survival deficit (D).

Interpretation:
1. Tumor dependency is most pronounced in young females with local cancer, since they depend most on their tumor. In other words they lack metastases that would protect them against tumor ablation.
2. Some females with regional disease carry metastases† and are less tumor dependent. In other words, their metastases protect †them from tumor ablation.
3. The negative survival deficit (C)† indicates that as disease progresses their prospect improves† (More on this topic v. conditional survival).
4. Since young patients with distant disease do not depend on their tumor anymore (they carry metastasis)† their prospect is the same as that of† older women (D).

Additional reading
Treatment promotes cancer progresion
Survival following cancer treatment
Pernicious cachexia

References

1.† Kathleen A. Cronin, Angela B. Mariotto, Lauren D. Clarke, Eric J. Feuer Chapter 5: Additional Common Inputs for Analyzing Impact of Adjuvant Therapy and Mammography on U.S. Mortality .
J Natl Cancer Inst Monogr 36: 26-29 (2006)

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